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The effect of cyclopiazonic acid on excitation‐contraction coupling in guinea‐pig ureteric smooth muscle: role of the sarcoplasmic reticulum
Author(s) -
Burdyga Theodor V.,
Wray Susan
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0855s.x
Subject(s) - cyclopiazonic acid , endoplasmic reticulum , guinea pig , contraction (grammar) , chemistry , smooth muscle , muscle contraction , coupling (piping) , anatomy , biophysics , medicine , biology , biochemistry , materials science , metallurgy
1 We have investigated the effect of cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum (SR) Ca 2+ ‐ATPase on excitation‐contraction (EC) coupling in guinea‐pig ureter, by measuring membrane currents, action potentials, intracellular [Ca 2+ ] and force. 2 CPA (20 μm) significantly enhanced the amplitude and duration of phasic contractions of ureteric smooth muscle associated with action potentials. This was accompanied by an increase in the duration of the intracellular Ca 2+ transient in intact tissue and single cells but not their amplitude. However, CPA also slowed the rate of rise, and fall, of the force and Ca 2+ transients. 3 Membrane potential recordings showed that CPA produced a small depolarization and a large increase in the duration of the plateau phase of the action potential. 4 Patch‐clamp studies showed marked inhibition of outward potassium current in the presence of CPA and an inhibition of spontaneous transient outward currents (STOCs). CPA had no effect on inward Ca 2+ current. 5 These data suggest that the SR plays a major role in modulating the excitability of the ureter, particularly via curtailing the action potential duration. This in turn will shorten the Ca 2+ transient and decrease force. This negative action on developed force predominates over any small role it may play in initiating force in the guinea‐pig ureter.