Rabbit intestinal smooth muscle calcium current in solutions with physiological calcium concentration

Abstract

SUMMARYThe calcium channel current in enzymatically isolated cells of the longitudinal muscle of rabbit jejunum was studied using the whole-cell voltage clamp technique. The current-voltage relationship was measured in cells held at potentials ranging from -90 to -30 mV in the presence of 1 5 mM-calcium or barium in order to test for the presence of multiple current components. The kinetics and current-voltage relationship of the current showed no evidence of a discrete low-threshold or 'transient' current. Measurable current was observed at -55 mV. Current availability was dependent on the holding potential but not on the test potential, suggesting the presence of only one type of calcium channel. A component of current persisted for at least 25 s following depolarization. Nifedipine reduced the Ca2" current amplitude without shifting the current-voltage relationship; the degree of inhibition was enhanced by depolarization of the holding potential. The peak and sustained currents were similarly inhibited by nifedipine. The results indicate the presence of a single type of dihydropyridine-sensitive calcium channel current which is partially activated at or near the physiological resting membrane potential of these cells.

Potential‐dependent inward currents in single isolated smooth muscle cells of the rat ileum.

“…HVA Ca2+ current HVA Caa2+ channels have been found in all SMCs studied previously (Kldckner & Isenberg, 1985;Ganitkevich, Shuba & Smirnov, 1986Caffrey et al 1986;Jmari et al 1986;Ohya et al 1986;Ame'dee et al 1987;Benham et al 1987;Aaronson 566 Ca2+ AND Nat CHANNELS IN SMOOTH MUSCLE et al 1988;Loirand et al 1989;Yamamoto et al 1989;Hisada, Kurachi & Sugimoto, 1990;Aaronson & Russell, 1991). They possess the following main features: (1) an apparent activation threshold usually in the voltage range between -40 and -20 mV in the presence of a physiological Ca2+ concentration; (2) dependence of the inactivation process both on Ca2+ ions and the membrane potential; (3) larger wholecell current and unitary conductances in the presence of Ba2+ rather than Ca2+ as a current carrier; and (4) high sensitivity to dihydropyridine antagonists.…”

“…Whole-cell and patch-clamp studies of single visceral SMCs have shown that the SMC membrane possesses only long-lasting or high-voltage-activated (HVA) Ca2`channel (Ganitkevich, Smirnov & Shuba, 1985;Mitra & Morad, 1985;Klickner & Isenberg, 1985;Ganitkevich, Shuba & Smirnov, 1986;Ohya, Terada, Kitamura & Kuriyama, 1986;Jmari, Mironneau & Mironneau, 1986;Yamamoto, Hu & Kao, 1989;Aaronson & Russell, 1991; but see Yoshino, Someya, Nishio, Yazawa, Usuki & Yabu, 1989). However, in contrast to visceral SMC, at least two populations, HVA and transient or low-voltage-activated (LVA) Ca2+ channels, were found in many vascular SMCs (Bean, Sturek, Puga & Hermsmeyer, 1986; Friedman, Suarez-Kurtz, Kaczorowski, Katz & Reuben, 1986;Hirst, Silverberg & van Helden, 1986;Loirand, Pacaud, Mironneau & Mironneau, 1986;Sturek & Hermsmeyer, 1986;Worley, Deitmer & Nelson, 1986;Benham, Hess & Tsien, 1987; Aaronson, Bolton, Lang & MacKenzie, 1988;McCarthy & Cohen, 1989;Ganitkevich & Isenberg, 1990; but see Caffrey, Josephson & Brown, 1986;Matsuda, Volk & Shibata, 1990).…”