Facilitation of Ca2+-channel currents in bovine adrenal chromaffin cells.
Ca2+-channel currents in primary cultures of bovine adrenal chromaffin cells were studied using the whole-cell patch-clamp method. Parameters of a double-pulse protocol were systematically varied to characterize facilitation by a prepulse (P1) of Ca2+-channel current during a test pulse (P2). The pulses were usually separated by 30 msec, an interval sufficient for decay of any measurable P1 tail currents. The Ca2+-channel current amplitude during P2 increased when P1 voltage was more positive than 0 mV. The effect became progressively greater with more positive P1 voltage. With a 60-msec P1 to +80 mV, the current amplitude typically increased by 25%-35% during a 60-msec P2. Comparison of facilitated and control inward Ca2+-channel current I(V) curves showed that facilitation was also strongly dependent on P2 test voltage. Facilitation of Ca2+-channel currents is a voltage-dependent phenomenon and is not dependent on Ca2+ entry. When short repetitive voltage-clamp pulses were applied, the Ca2+-channel current amplitude increased with each pulse. This suggests that Ca2+-channel facilitation could enhance release of catecholamines from chromaffin cells during a train of action potentials.
D000313:Adrenal Medulla / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects
D007473:Ion Channels; D001464:Barium; D002118:Calcium