Characterization of action potential-triggered [Ca2+]i transients in single smooth muscle cells of guinea-pig ileum
Article first published online: 11 FEB 2009
1997 British Pharmacological Society
British Journal of Pharmacology
Volume 122, Issue 3, pages 477–486, October 1997
How to Cite
Kohda, M., Komori, S., Unno, T. and Ohashi, H. (1997), Characterization of action potential-triggered [Ca2+]i transients in single smooth muscle cells of guinea-pig ileum. British Journal of Pharmacology, 122: 477–486. doi: 10.1038/sj.bjp.0701407
- Issue published online: 11 FEB 2009
- Article first published online: 11 FEB 2009
- (Received April 4, 1997, Revised June 20, 1997, Accepted June 30, 1997)
- Action potential;
- excitation-contraction coupling;
- Ca2+-induced Ca2+ release;
- smooth muscle;
- guinea-pig ileum
- 1To characterize increases in cytosolic free Ca2+ concentration ([Ca2+]i) associated with discharge of action potentials, membrane potential and [Ca2+]i were simultaneously recorded from single smooth muscle cells of guinea-pig ileum by use of a combination of nystatin-perforated patch clamp and fura-2 fluorimetry techniques.
- 2A single action potential in response to a depolarizing current pulse elicited a transient rise in [Ca2+]i. When the duration of the current pulse was prolonged, action potentials were repeatedly discharged during the early period of the pulse duration with a progressive decrease in overshoot potential, upstroke rate and repolarization rate. However, such action potentials could each trigger [Ca2+]i transients with an almost constant amplitude.
- 3Nicardipine (1 μM) and La3+ (10 μM), blockers of voltage-dependent Ca2+ channels (VDCCs), abolished both the action potential discharge and the [Ca2+]i transient.
- 4Charybdotoxin (ChTX, 300 nM) and tetraethylammonium (TEA, 2 mM), blockers of large conductance Ca2+-activated K+ channels, decreased the rate of repolarization of action potentials but increased the amplitude of [Ca2+]i transients.
- 5Thapsigargin (1 μM), an inhibitor of SR Ca2+-ATPase, slowed the falling phase and somewhat increased the amplitude, of action potential-triggered [Ca2+]i transients without affecting action potentials. In addition, in voltage-clamped cells, the drug had little effect on the voltage step-evoked Ca2+ current but exerted a similar effect on its concomitant rise in [Ca2+]i to that on the action potential-triggered [Ca2+]i transient.
- 6Similar action potential-triggered [Ca2+]i transients were induced by brief exposures to high-K+ solution. They were not decreased, but rather increased, after depletion of intracellular Ca2+ stores by a combination of ryanodine (30 μM) and caffeine (10 mM) through an open-lock of Ca2+-induced Ca2+ release (CICR)-related channels.
- 7The results show that action potentials, discharged repeatedly during the early period of a long membrane depolarization, undergo a progressive change in configuration but can each trigger a constant rise in [Ca2+]i. Intracellular Ca2+ stores have a role, especially in accelerating the falling phase of the action potential-triggered [Ca2+]i transients by replenishing cytosolic Ca2+. No evidence was provided for the involvement of CICR in the action potential-triggered [Ca2+]i transient.
British Journal of Pharmacology (1997) 122, 477–486; doi:10.1038/sj.bjp.0701407