Two calcium currents in a smooth muscle cell line.
Membrane currents in small cells of a smooth muscle cell line (A10) derived from embryonic rat thoracic aorta were monitored by the patch electrode whole-cell voltage clamp technique. Three currents, two divalent cation currents, and a Ca2+-activated K+ current have been observed. The latter is readily abolished pharmacologically, allowing the characterization of the divalent cation currents. With a holding potential of -50 mV, a single divalent current, which inactivates slowly, is elicited on depolarization of the membrane potential to values positive to ca. -10 mV. The second divalent cation current is only observed when the holding potential is negative to -55 mV and the membrane is pulsed to values positive to ca. -35 mV. This current is rapidly inactivating, peaking in approximately 5 ms and decaying with a t1/2 of ca. 15 ms at 0 mV when conveyed by Ba2+. The rapidly inactivating divalent cation current is depressed by substitution of Ba2+ for Ca2+ in the bathing solution and is highly insensitive to organic Ca2+ channel blockers. The slowly inactivating channel has more typical characteristics of Ca2+ channels; it is more permeable to Ba2+ than to Ca2+ and is sensitive to modulation by dihydropyridines. These data demonstrate the presence of two distinctly different Ca2+ channels in A10 cells.
M E
ME
Friedman
G
G
Suarez-Kurtz
G J
GJ
Kaczorowski
G M
GM
Katz
J P
JP
Reuben
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000502:physiology*; D009543:Nifedipine / Q000031:analogs & derivatives / Q000494:pharmacology; D015737:Nisoldipine; D011188:Potassium / Q000502:physiology; D051381:Rats; D012508:Sarcolemma / Q000502:physiology
D007473:Ion Channels; D015737:Nisoldipine; D009543:Nifedipine; D011188:Potassium; D002118:Calcium