The effect of high [K(+)]o on spontaneous Ca(2+) waves in freshly isolated interstitial cells of Cajal from the rabbit urethra

Interstitial cells of Cajal (ICC) act as putative pacemaker cells in the rabbit urethra. Pacemaker activity in ICC results from spontaneous global Ca²⁺ waves that can be increased in frequency by raising external [K⁺]. The purpose of this study was to elucidate the mechanism of this response. Intracellular [Ca²⁺] was measured in fluo‐4‐loaded smooth muscle cells (SMCs) and ICC using a Nipkow spinning disk confocal microscope. Increasing [K⁺]_o to 60 mmol/L caused an increase in [Ca²⁺]_i accompanied by contraction in SMCs. Raising [K⁺]_o did not cause contraction in ICC, but the frequency of firing of spontaneous calcium waves increased. Reducing [Ca²⁺]_o to 0 mmol/L abolished the response in both cell types. Nifedipine of 1 μmol/L blocked the response of SMC to high [K⁺]_o, but did not affect the increase in firing in ICC. This latter effect was blocked by 30 μmol/L NiCl₂ but not by the T‐type Ca²⁺ channel blocker mibefradil (300 nmol/L). However, inhibition of Ca²⁺ influx via reverse‐mode sodium/calcium exchange (NCX) using either 1 μmol/L SEA0400 or 5 μmol/L KB‐R7943 did block the effect of high [K⁺]_o on ICC. These data suggest that high K⁺ solution increases the frequency of calcium waves in ICC by increasing Ca²⁺ influx through reverse‐mode NCX.

Pacemaker activity in ICC results from spontaneous global Ca²⁺ waves that can be increased in frequency by raising external [K⁺]. The experiments described support the hypothesis that high K⁺ solution increases the frequency of calcium waves in ICC by increasing Ca²⁺ influx through reverse‐mode NCX.

[Relation between plasma Ara-C and intracellular Ara-CTP levels by intermediate dose and high dose Ara-C administration in the treatment of AML]

Plasma level of cytosine arabinoside (Ara-C) and intracellular cytosine arabinoside triphosphate (Ara-CTP) in peripheral blood and bone marrow were measured in 8 patients with non treated acute myelogenous leukemia. Ara-C was administered by 1 hr infusion (3 g/m2 and 500 mg/m2) and was followed for 12 hrs. The AUC of Ara-C in plasma following 3 g/m2 infusion were greater than the 500 mg/m2 (p less than 0.05). Intracellular Ara-CTP in peripheral blood following 3 g/m2 and 500 mg/m2 infusions were on the same level, after 1 hr. But AUC of intracellular Ara-CTP following 3 g/m2 infusion was greater than 500 mg/m2. There was a correlation between AUC of Ara-C in the peripheral blood (p less than 0.01). Intracellular Ara-CTP in the bone marrow and peripheral blood showed a similar level. Intracellular Ara-CTP in bone marrow was lower than in peripheral blood, however, there was no correlation between intracellular Ara-CTP in bone marrow and in peripheral blood.