The effect of ions on the cutaneous sensory endings of the frog

ADAPTATION OF CUTANEOUS TACTILE RECEPTORS : VI. INHIBITORY EFFECTS OF POTASSIUM AND CALCIUM

1. Both solutions of Ringer plus fifteen times the normal K content, and solutions of Ringer plus fifteen times the normal Ca content markedly hasten the adaptation of single freely branching axon endings in frog's skin to repetitive air puff stimuli. 2. The K effect is produced more rapidly than is that of Ca. The K effect is reversible by washing with Ringer's solution, while the Ca effect is not. The Ca inhibition can, however, be reversed and recovery effected by washing with K rich solutions. 3. Evidence is discussed which indicates that Ca probably plays no rôle in normal adaptation, and the experiments are interpreted as substantiating the hypothesis of adaptation due to K.

Influence of nifedipine on arterial baroreflex modulation of heart rate control during dynamic increases in arterial pressure: studies in normal man

Studies in animals have demonstrated that calcium channel blocking agents exert important influences on autonomic mechanisms in addition to their direct vascular effects. Previous studies in our laboratory showed that clinical doses of nifedipine sensitized baroreceptor-mediated control of peripheral vascular resistance in normal human subjects. However, baroreflex control of vascular tone does not necessarily imply parallel control of heart rate. A series of experiments was therefore performed to test the hypothesis that therapeutic doses of nifedipine would potentiate arterial baroreflex modulation of heart rate during ramp increases of arterial pressure in normal volunteers. Arterial baroreflex control was assessed by measuring heart interval (HI) responses to dynamic ramp elevation of systolic arterial pressure (SAP) with bolus administration of phenylephrine (PE) before and after nifedipine or placebo in 19 normal subjects. Arterial baroreflex control was calculated from the slope of the regression of SAP on succeeding HI during the first 18 cardiac cycles following onset of rise of SAP after PE bolus. In 13 subjects, bolus PE produced an increase in SAP from 125 +/- 3 mm Hg to 152 +/- 5 mm Hg (p less than 0.01), with a resultant increase in HI from 1110 +/- 57 msec to 1541 +/- 87 msec (p less than 0.01). The baroreflex response was linear (r greater than 0.80, p less than 0.025) and = 17.8 +/- 3.3 msec/mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nifedipine on baroreflex modulation of vascular resistance in man

Studies in animals have demonstrated that, in addition to their vascular effects, calcium channel blockers have important effects on baroreceptor function. We performed a series of experiments to determine if nifedipine, in doses employed clinically, alters baroreflex control of vascular resistance in normal humans. Forearm vasoconstrictor responses of 14 normal subjects to unloading of baroreceptors with lower body negative pressure (LBNP), to a cold pressor test and during intra-arterial infusions of norepinephrine were studied in the control state and following administration of nifedipine. Nifedipine had no effect on baseline mean arterial pressure or central venous pressure. Heart rate and forearm blood flow (FBF) increased significantly following nifedipine: heart rate = 59.7 +/- 2.4 bpm before and 72.6 +/- 4.4 bpm after nifedipine (mean +/- SE, p less than 0.001, n = 14); FBF = 4.6 +/- 0.4 ml X min-1 X 100 ml-1 before and 6.7 +/- 1.0 ml X min1 X 100 ml-1 after nifedipine (p less than 0.02, n = 14). Forearm vascular resistance (FVR) tended to decrease following nifedipine but the difference was not significant: FVR = 21.1 +/- 1.4 units before and 17.8 +/- 2.3 units after nifedipine (p = 0.07, n = 14). Nifedipine attenuated forearm vasoconstrictor responses to cold pressor stimulus: delta FVR during cold pressor test = +10.3 +/- 2.4 units before and +4.7 +/- 1.4 units after nifedipine (p less than 0.02, n = 14). Likewise, nifedipine depressed vasoconstrictor responses to intra-arterial infusion of norepinephrine: delta FVR during norepinephrine = +15.5 +/- 3.4 units before and +10.2 +/- 2.9 units after nifedipine (p less than 0.05, n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium and magnesium sensitivity of the carotid baroreceptor reflex in cats

The systemic blood pressure response to changes in carotid sinus pressure has been examined during variations in the calcium and magnesium concentration of the perfusate of the isolated sinus. The threshold for the blood pressure response was increased by 16 +/- 0.8% when calcium was raised from 1.1 mM (control) to 2.2 mM and increased by 27 +/- 1.8% when calcium was raised to 3.3 mM. The threshold was reduced by 21 +/- 0.7% in zero calcium and 13 +/- 0.8% in 0.55 mM Ca2+. The sensitivity (slope of the linear portion of the pressure response curve) of the reflex was not significantly changed except at 3.3 mM Ca2+ where it was reduced by 16 +/- 2.9%. Magnesium had directionally similar effects of a lesser magnitude. Earlier work described the reduced sensitivity and threshold of the baroreceptor reflex when sodium concentration in the carotid perfusate was reduced. The present study shows that reducing calcium attenuates the effect of lowered sodium and increasing calcium augments it. These results are discussed in terms of possible ionic influences on the receptor potential and spike generation.