Parathyroid hormone selectively inhibits L-type calcium channels in single vascular smooth muscle cells of the rat

Association between Parathyroid Hormone and Cardiovascular Disease

Although parathyroid hormone is known to be related with calcium and phosphate metabolism, it has been also reported to have several effects on the cardiovascular system including heart and vessels. However, the detailed pathophysiological mechanisms remain unclear. Clinical studies have indicated that parathyroid hormone is associated with cardiovascular events and mortality not only in patients with chronic kidney disease but also in those without chronic kidney disease. As a possible mechanism, it is thought that parathyroid hormone is associated with the renin-angiotensin-aldosterone system and has direct effects on the cardiovascular system. Therefore, we should pay attention to not only the control of serum phosphate and calcium levels but also the control of serum parathyroid hormone levels, especially in patients with chronic kidney disease.

N-terminal parathyroid hormone-related peptide hyperpolarizes endothelial cells and causes a reduction of the coronary resistance of the rat heart via endothelial hyperpolarization

Parathyroid hormone-related peptide (PTHrP) is known to be a strong vasorelaxant peptide. The mechanisms by which PTHrP reduces the coronary resistance of the rat heart have not been worked out but seem to be independent of the classical PTH/PTHrP receptor-mediated, cAMP-dependent effect. In this study we hypothesized that PTHrP reduces the coronary resistance of the rat heart via endothelial cell hyperpolarization. Isolated microvascular endothelial cells from rat heart were incubated with PTHrP(1-36), and changes in the membrane potential were recorded via DiBAC fluorescence. Cells exposed to PTHrP showed a hyperpolarization of approximately 7mV. In the isolated Langendorff preparation, PTHrP-dependent vasodilatation of l-nitro-arginine-exposed hearts was abolished under depolarizing conditions (high potassium). Denudation of the endothelial cell layer significantly impaired the vasodilatory effect of PTHrP. In the presence of H89 (a cAMP/protein kinase A pathway antagonist) and indomethacin (a cyclooxygenase inhibitor), PTHrP dilated the vessels. In conclusion, PTHrP exerted a nitric oxide-independent vasodilatory effect that depends on endothelial cell hyperpolarization.

Relaxant mechanisms of parathyroid hormone in rat mesenteric artery

The effects of parathyroid hormone (PTH) on tension and intracellular Ca level ([Ca ] ) were examined in ring preparations of rat mesenteric artery using isometric tension recording and the fura-2 method, respectively. The PTH (30 n ) elicited relaxation in arterial rings precontracted by phenylephrine regardless of the presence or absence of endothelium. In the endothelium-denuded arterial rings precontracted by 3 micro M of phenylephrine or 60 m of potassium chloride (KCl), PTH-related protein and PTH produced concentration-dependent relaxation to the same extent, but inhibited contraction induced by phenylephrine more effectively than that induced by KCl. Phenylephrine-induced tonic contraction was changed to a phasic one with decreased peak tension in the presence of PTH. Similar changes were observed with extracellular Ca removal or methoxyverapamil plus SK&F96365, respective of voltage-gated and receptor-operated Ca channel inhibitors. Phenylephrine evoked a concentration-dependent contraction concomitant with an increase in [Ca ]. PTH reduced both responses to the same extent. In a Ca -free solution, PTH inhibited a phasic contraction and a transient increase in [Ca ] in response to phenylephrine but not caffeine. Reverse transcriptase-polymerase chain reaction showed that PTH and PTH receptors were expressed in the rat mesenteric artery. In this tissue, PTH increased cyclic adenosine monophosphate (cAMP) levels. These results suggest that the inhibitory effect of PTH on alpha -adrenoceptor-mediated contraction results from the inhibition of Ca influx through receptor-operated and voltage-gated Ca channels, and Ca release from Ca stores, probably via increased cAMP in the rat mesenteric artery.

Characterization of voltage-gated calcium currents in freshly isolated smooth muscle cells from rat tail main artery

The aim of the present study was to characterize voltage-gated Ca2+ currents in smooth muscle cells freshly isolated from rat tail main artery in the presence of 5 mmol L(-1) external Ca2+. Calcium currents were identified on the basis of their voltage dependencies and sensitivity to nifedipine, Ni2+ and cinnarizine. In the majority of the cells studied, T- and L-type currents were observed, while the remaining cells showed predominantly L-type currents. In the latter group of cells, holding potential change from -50 to either -70 or -90 mV increased the corresponding inward current amplitude while its voltage activation threshold remained unchanged. The steady state inactivation of L-type Ca2+ channels showed half-maximal inactivation at -38 mV. A Ca2+-dependent inactivation was also evident. Nifedipine (3 micromol L(-1)) blocked L-type but not T-type Ca2+ currents. Ni2+ (50 micromol L(-1)) as well as cinnarizine (1 micromol L(-1)) suppressed the nifedipine-resistant, T-type component of the currents. At higher concentrations, both Ni2+ (0.3-1 mmol L(-1)) and cinnarizine (10 micromol L(-1)) blocked the net inward current. Replacement of Ca2+ with 10 mmol L(-)1 Ba2+ significantly increased the amplitude of L-type Ca2+ currents. These results demonstrate that smooth muscle cells freshly isolated from rat tail main artery may be divided into two populations, one expressing both L- and T-type and the other only L-type Ca2+ channels. Furthermore, this report shows that in arterial smooth muscle cells cinnarizine potently inhibited T-type currents at low concentrations (1 micromol L(-1)) but also blocked L-type Ca2+ currents at higher concentrations (10 micromol L(-1)).

Vascular Effects of Progesterone : Role of Cellular Calcium Regulation

-Vascular actions of progesterone have been reported, independently of estrogen, affecting both blood pressure and other aspects of the cardiovascular system. To study possible mechanisms underlying these effects, we examined the effects of P in vivo in intact rats and in vitro in isolated artery and vascular smooth muscle cell preparations. In anesthetized Sprague-Dawley rats, bolus intravenous injections of P (100 µg/kg) significantly decreased pressor responses to norepinephrine (0.3 µg/kg). In vitro, progesterone (10(-8) to 10(-5) mmol/L) produced a significant, dose-dependent relaxation of isolated helical strips, both of rat tail artery precontracted with KCl (60 mmol/L) or arginine vasopressin (3 nmol/L), and of rat aorta precontracted with KCl (60 mmol/L) or norepinephrine (0.1 µmol/L). In isolated vascular smooth muscle cells, progesterone (5x10(-)(7) mol/L) reversibly inhibited KCl (30 mmol/L) -induced elevation of cytosolic-free calcium by 64.1+/-5.5% (P:<0.05), and in whole-cell patch-clamp experiments, progesterone (5x10(-6) mol/L) reversibly and significantly blunted L-type calcium channel inward current, decreasing peak inward current to 65.7+/-4.3% of the control value (P:<0.05). Our results provide evidence that progesterone is a vasoactive hormone, inhibiting agonist-induced vasoconstriction. The data further suggest that progesterone effects on vascular tissue may, at least in part, be mediated by modulation of the L-type calcium channel current activity and, consequently, of cytosolic-free calcium content.

Altered L-type Ca(2+) channel currents in vascular smooth muscle cells from experimental diabetic rats

Vascular complications of diabetes are associated with abnormal Ca(2+) handling by vascular smooth muscle cells (SMCs) in which the alteration in L-type voltage-dependent Ca(2+) channel (VDCC) currents may play an important role. In the present study, the characteristics of L-type VDCC currents in tail artery SMCs from streptozotocin-induced diabetic rats were examined. The densities, but not the voltage dependence, of L-type VDCC currents were reduced as diabetes progressed from 1 wk to 3 mo. The inhibitory effect of dibutyryl-cAMP on L-type VDCC currents was greater in diabetic SMCs than in age-matched control cells (P < 0.01). Both the stimulatory effect of BAY K 8644 and the inhibitory effect of nifedipine on L-type VDCC currents were significantly enhanced in diabetic cells. The diabetes-related abnormalities in L-type VDCC currents were mimicked by culturing SMCs with a high concentration of glucose. Our results suggest that the properties of L-type VDCC in diabetic vascular SMCs were significantly altered, partially related to the increased L-type VDCC sensitivity to cAMP and hyperglycemia.

Three different vasoactive responses of rat tail artery to nicotine

The vasoactive effects of nicotine on isolated rat tail artery tissues were studied. Nicotine transiently contracted rat tail artery tissues (EC50, 55.6 ± 2 µM) in an extracellular Ca2+ dependent and endothelium-independent fashion. The blockade of alpha1-adrenoceptors, but not alpha2-adrenoceptors or P2X purinoceptors, inhibited the nicotine-induced contraction by 38 ± 7% (p < 0.05). Nicotine (1 mM) depolarized membrane by 13 ± 3 mV, but did not affect L-type Ca2+ channel currents, of the isolated rat tail artery smooth muscle cells. The phenylephrine-precontracted tail artery tissues were relaxed by nicotine (EC50, 0.90 ± 0.31 mM), which was significantly inhibited after the blockade of nicotinic receptors. Simultaneous removal of phenylephrine and nicotine, after a complete relaxation of the phenylephrine-precontracted tail artery strips was achieved by nicotine at accumulated concentrations (>=10 mM), triggered a Ca2+-dependent rebound long-lasting vasoconstriction (n = 20). This rebound contraction was abolished in the absence of calcium or in the presence of tetracaine in the bath solution. Pretreatment of vascular tissues with a nicotinic receptor antagonist did not affect the nicotine-induced vasoconstriction or nicotine withdrawal induced rebound contraction. The elucidation of the triphasic vascular effects of nicotine and the underlying mechanisms is important for a better understanding of the complex vascular actions of nicotine.Key words: nicotine, smokeless tobacco, vascular smooth muscles, contraction, relaxation.

Effects of excess PTH on nonclassical target organs

The classical target organs for parathyroid hormone (PTH) are the bone and kidneys. In uremia, however, numerous studies have shown that PTH may also affect the function of a number of nonclassical organs and tissues besides the bone and kidney, including the brain, heart, smooth muscles, lungs, erythrocytes, lymphocytes, pancreas, adrenal glands, and testes. Most of these effects do not apply to the generally accepted actions or normal regulatory mechanisms of PTH. Thus, the potential role of PTH as one of the possibly many toxins in uremia is of current interest. The molecular basis for the actions of elevated PTH levels on various nonrenal and nonskeletal organs or tissues might be mediated via the widespread distribution of the classical PTH/PTH-related peptide (PTHrP) receptors and via the novel PTH2 receptors. The present survey deals with an evaluation of the nonrenal and nonskeletal effects of excess PTH in uremia, taking into consideration the presently available information on the organ-specific expression of the classical and novel PTH receptors, and of the expression and function of PTHrP.

Actions of neurotransmitters and other messengers on Ca2+ channels and K+ channels in smooth muscle cells

Ion channels play key roles in determining smooth muscle tone by setting the membrane potential and allowing Ca2+ influx. Perhaps not surprisingly, therefore, they also provide targets for neurotransmitters and other messengers that act on smooth muscle. Application of patch-clamp and molecular biology techniques and the use of selective pharmacology has started to provide a wealth of information on the ion channel systems of smooth muscle cells, revealing complexity and functional significance. Reviewed are the actions of messengers (e.g., noradrenaline, acetylcholine, endothelin, angiotensin II, neuropeptide Y, 5-hydroxytryptamine, histamine, adenosine, calcitonin gene-related peptide, substance P, prostacyclin, nitric oxide and oxygen) on specific types of ion channel in smooth muscle, the L-type calcium channel, and the large conductance Ca(2+)-activated, ATP-sensitive, delayed rectifier and apamin-sensitive K+ channels.

Human fetal membranes inhibit calcium L-channel activated uterine contractions

OBJECTIVE

Paracrine signals among fetal membranes, decidua, and uterus play an important role in the initiation of parturition in women. In previous work we demonstrated that fetal membranes inhibit uterine contractions. In the current study we test the hypothesis that the fetal membranes decrease uterine contractions by inhibition of the uterine calcium L-channel.

STUDY DESIGN

Our dual-chamber fetal membrane-uterine muscle in vitro model was used in this study. Rat uterine muscle strips were anchored into the maternal sides of the chambers. Fetal membranes (or Parafilm controls) were added to the chamber in a removable cassette. Uterine contractions were stimulated with the specific calcium L-channel agonist Bay K 8644.

RESULTS

When uterine muscle was exposed to full-thickness fetal membranes (amnion-chorion with attached decidua) or to the intact fetal components (chorion-amnion) or to chorion alone, the Bay K 8644 dose-response curve was significantly shifted to the right. When uterine muscle was exposed to amnion alone or to the decidua alone, the Bay K 8644 dose-response curve was not shifted. Fetal membranes, did not cause a shift in the ionomycin (a calcium ionophore) dose-response curve.

CONCLUSION

These results support the hypothesis and provide evidence that human fetal membranes, most likely chorion, release an endogenous calcium L-channel inhibitor.

cAMP signaling inhibits dihydropyridine-sensitive Ca2+ influx in vascular smooth muscle cells

This study examines the role of the cAMP signaling pathway in the regulation of 45Ca influx in cultured vascular smooth muscle cells from the rat aorta. K+o-induced depolarization of smooth muscle cells increased the rate of 45Ca uptake by twofold to threefold. This effect was completely abolished by the dihydropyridine derivatives nifedipine and nicardipine, with a Ki of 3 and 10 nmol/L, respectively. Activators of cAMP signaling (isoproterenol, forskolin, cholera toxin) increased cAMP content by 50- to 100-fold and decreased voltage-dependent 45Ca uptake by 50% to 70%. Neither the dihydropyridines nor the cAMP activators affected basal 45Ca influx. Direct addition of the protein kinase inhibitor H-89 to the incubation medium in the 1- to 10-micromol/L range did not alter basal 45Ca uptake but completely abolished voltage-dependent Ca2+ transport. Preincubation of cells for 1 hour with 10 micromol/L H-89 did not modify basal and depolarization-induced 45Ca uptake in H-89-free medium but prevented forskolin-induced inhibition of voltage-dependent Ca2+ influx. The addition of cytoskeleton-active compounds reduced voltage-dependent Ca2+ transport and completely abolished its regulation by cAMP. Activation of cAMP signaling decreased the volume of smooth muscle cells by 12% to 15%. The same cell volume diminution in hyperosmotic medium did not alter voltage-dependent 45Ca uptake. Thus, data obtained in this study show that in contrast to cardiac and skeletal myocytes, in vascular smooth muscle cells, 45Ca influx, putatively due to L-type channels, is inhibited by cAMP. This regulatory pathway appears to be mediated via protein kinase A activation and cytoskeleton reorganization.

Effects of three fragments of parathyroid hormone on calcium channel currents in neonatal rat ventricular cells

The effects of different fragments of bovine parathyroid hormone, bPTH-(1-34), bPTH-(1-84) and bPTH-(3-34), on two types of calcium channel currents in neonatal rat ventricular cells were compared in the present study. bPTH-(1-34) increased the amplitude of L channel currents, but not of the T channel currents. This effect of bPTH-(1-34) was sustained after a complete washout of the peptide from the bath. The intact PTH molecule, bPTH-(1-84), also increased L channel currents but not affecting T channel currents. While bPTH-(3-34) did not affect the amplitudes of either L or T channel currents by itself, pretreatment of cells with bPTH-(3-34) abolished the effects of both bPTH-(1-34) and bPTH-(1-84) on L channel currents. Moreover, the kinetics of L channel currents in the presence of bPTH-(1-34) or bPTH-(3-34) were different. bPTH-(1-34) increased the time constant of activation, but not of inactivation, of L channel currents from 1.8 to 2.5 ms (P < 0.05). In contrast, bPTH-(3-34) decreased the time constant of inactivation, but not of activation, of L channel currents from 159 to 117 ms (P < 0.05). These results indicate that different fragments of PTH exert different effects on the amplitudes or kinetics of cardiac calcium channel currents.

Dual modulation of the L-type calcium current of rat osteoblastic cells by parathyroid hormone: opposite effects of protein kinase C and cyclic nucleotides

Using whole-cell voltage-clamp recording of rat osteoblastic cells, we show that PTH-(1-34), known to stimulate protein kinase C (PKC) and adenylate cyclase, has a dual effect on the L-type calcium current. It induces a long-lasting increase and a superimposed reversible decrease, which can be separated by repeating hormone applications. The stimulatory effect is the only effect induced by the (3-34) fragment, able to stimulate PKC but unable to stimulate adenylate cyclase. The L current is stimulated by an active phorbol ester and is reduced by permeable analogues of cyclic AMP. Thus, the effect of PTH-(1-34) can be explained by the opposite effects of PKC and cyclic AMP. Dibutyryl cyclic GMP reduces the L current even more potently than dibutyryl cyclic AMP. The above modulations are all voltage-insensitive. These results led us to reinvestigate the effects of some vitamin D3 metabolites known to stimulate PKC and/or guanylate cyclase, and previously reported to affect the voltage-sensitivity of the L current. We only detected voltage-insensitive effects.

PHF: the new parathyroid hypertensive factor

Parathyroid Hypertensive Factor (PHF) was discovered in SHR rats as a circulating substance with a unique delayed (60-90 min) hypertensive effect when injected into a normotensive assay rat. Subsequently, this correlation with hypertension was established in humans, especially in low-renin, salt-sensitive patients. Animal model studies also confirmed this correlation. Endocrinectomy and glandular replacement studies suggested that the parathyroid gland was the source of PHF. Subsequently, glands and cells in culture were also shown to secrete the substance. Other studies verified the parathyroid origin of PHF. The mechanism of action of PHF was shown to rely mainly on the opening of L-type calcium channels in vascular smooth muscle cells with an increase in [Ca2++]i. It is known that diseases other than hypertension often show increased [Ca2++]i and clinical features similar to hypertension, among them Type II diabetes. A recent study shows a correlation between circulating PHF level and Type II diabetes irrespective of the blood pressure status of the patient. It is suggested that PHF may be a [Ca++]i modulator, an excessive amount of which in the circulation may act on various target tissues, resulting in various disease symptoms with hypertension as an example. There may be many other such PHF-related diseases yet to be identified.

Parathyroid hormone-related peptide may increase mammary blood flow

Amino-terminal fragments of PTHrP were previously shown to increase regional blood flow in laboratory animals. Since PTHrP is produced in the lactating mammary gland and associated nutrient vessels, we examined the effects of peptide fragments of PTHrP on the hemodynamics of the mammary gland of dried sheep. The left arterial mammary blood flow measured using ultrasonic flow probes in four dried Lacaune ewes was 233 +/- 11 ml/minute. It was significantly increased when synthetic human PTHrP-(1-34) or (1-86) fragments were injected into the mammary artery. The effect was dose dependent for PTHrP-(1-34), varying between 0.0075 and 0.3 nmol/kg body weight. PTHrP-(140-173) fragment lacked any vasorelaxant activity. Synthetic human endothelin (ET1) decreased arterial blood flow in a dose-dependent manner. This decrease was inhibited by PTHrP-(1-34), and this inhibition was PTHrP dose related. When ET1 (10 pmol/kg body weight) was injected together with PTHrP-(1-86) (100 pmol/kg body weight), only a significant increase in mammary blood flow was observed. Thus, PTHrP produced by the lactating mammary gland may be involved in the regulation of mammary blood flow.

Renin stimulating properties of parathyroid hormone-related peptide in the isolated perfused rat kidney

Previous studies showed that PTHrP exhibits renal vasodilating, arteriolar cAMP stimulating and receptor binding properties. The present experiments were designed to study whether PTHrP may influence renin secretion. Rat kidneys were isolated and single-pass perfused at constant flow and stabilized pressure. Exposures to PTHrP or PTH stimulated a dose-dependent renin release reaching similar Vmax. The affinity (0.1 nM) and threshold concentration (0.01 nM) for PTHrP were about 10 times lower than for PTH. Compared to 10 microM isoproterenol, the maximum renin responses to PTHrP were similar but of shorter duration. The PTHrP dose-response curve was not affected by 10 microM indomethacin. Administered simultaneously, PTHrP and PTH displayed no additive effects. PTHrP-induced renin release as well as the role of extracellular calcium were further studied in nonfiltering kidneys, which were perfused at a constant flow and stable pressure in a closed circuit. Basal renin release was inversely related with perfusate calcium and was depressed by the calcium ionophore BAY-K8644. PTHrP (100 nM) induced a 1.6-fold increase of basal renin release in normocalcic perfusate. Removing calcium abolished renin responses. PTHrP reversed the inhibiting effects of hypercalcic media or BAY-K8644 on basal renin release. The results support calcium-mediated renin stimulating properties for PTHrP, via PTH receptors, independently from baroreceptors, macula densa and prostaglandins.

Inhibitory effects of histamine and bradykinin on calcium current in smooth muscle cells isolated from guinea-pig ileum

1. Single smooth muscle cells were isolated from the longitudinal muscle layer of the guinea-pig ileum and within 10 h Ca(2+)-currents (ICa) were recorded using the whole-cell patch clamp technique. 2. Histamine (10 microMs) and bradykinin (BK, 1 microM) suppressed ICa; the effect had two phases: a rapid and transient suppression of ICa followed by a sustained suppression. Acetylcholine and substance P appeared to have similar effects but these were not investigated in detail. 3. The effects of histamine and BK on ICa were established by high intracellular concentrations of the Ca2+ buffer EGTA (30 mM) or 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) (5 mM) in the absence of Ca2+ added to the pipette solution. When [Ca2+]i was strongly buffered to 125 or 190 nM by BAPTA-Ca2+ mixtures in the pipette the transient suppression of ICa was blocked but the sustained effect still occurred. This indicated that the transient effect was caused by a rise in [Ca2+]i. The sustained effect, in contrast, did not seem to be caused by a rise in [Ca2+]i but did show Ca2+ dependence because it did not occur if [Ca2+]i was abnormally low. 4. Application of caffeine (10 mM) to deplete stored Ca2+ or intracellular heparin (1 mM) to block the action of D-myo-inositol 1,4,5-trisphosphate (IP3) to release stored Ca2+ prevented the transient but not the sustained suppression of ICa. Heparin also blocked the transient Ca(2+)-activated K+ current in response to histamine or BK. Both transient and sustained suppressions of Ca2+ channel activity were observed in the absence of extracellular Ca2+ when current was carried mostly by Na+ ions. 5. Intracellular guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S; 10 or 100 microM) induced a gradual decline of ICa upon which transient decreases of current were superimposed. Histamine caused a larger than normal inhibition of ICa and no recovery occurred on wash-out. Intracellular guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S; 1 mM) abolished the effects of histamine and BK on ICa.(ABSTRACT TRUNCATED AT 400 WORDS)

The changes in contractile status of single vascular smooth muscle cells and ventricular cells induced by bPTH-(1-34)

Single smooth muscle cells from rat tail artery and ventricular myocytes from neonatal rat were isolated by repeated enzyme digestion. The change in cell area as determined photographically was used as an index of cell contraction. The photographic areas of single smooth muscle cells bathed in normal Tyrode solution were 403 +/- 22 (n = 13) square micra. Exposure of smooth muscle cells to a modified Tyrode solution containing 60 mM KCl induced cell contraction. This contraction was inhibited by bPTH-(1-34) at a concentration of 1 microM. The inhibitory effect of bPTH-(1-34) was time-dependent with maximum inhibition at 5 min after administration. The photographic areas of ventricular myocytes bathed in the culture medium without fetal calf serum were 516 +/- 47 (n = 29) square micra. At a concentration of 1 microM, bPTH-(1-34) produced a time-dependent contraction in ventricular myocytes as shown by the decrease in the photographic cell area (88 +/- 2% of the control value at 15 min, n = 9, p < 0.01). Furthermore, 1 microM nifedipine inhibited the effect of bPTH-(1-34) on the contraction of ventricular myocytes, indicating that bPTH-(1-34) might exert its action via a calcium channel related mechanism. In addition, bPTH-(1-34) increased the contraction frequency of single ventricular cells, which could also be inhibited by nifedipine. The present study suggests that bPTH-(1-34) directly relaxes precontracted single vascular smooth muscle cells and contracts single ventricular myocytes.

Calcium ion homeostasis in smooth muscle

Ca2+ plays an important role in the regulation of smooth-muscle contraction. In this review, we will focus on the various Ca(2+)-transport processes that contribute to the cytosolic Ca2+ concentration. Mainly the functional aspects will be covered. The smooth-muscle inositol 1,4,5-trisphosphate receptor and ryanodine receptor will be extensively discussed. Smooth-muscle contraction also depends on extracellular Ca2+ and both voltage- and Ca(2+)-release-activated plasma-membrane Ca2+ channels will be reviewed. We will finally discuss some functional properties of the Ca2+ pumps that remove Ca2+ from the cytoplasm and of the Ca2+ regulation of the nucleus.