Imaging of Ca2+ release by caffeine and 9-methyl-7-bromoeudistomin D and the associated activation of large conductance Ca2+-dependent K+ channels in urinary bladder smooth muscle cells of the guinea pig.
Ca2+ release by caffeine and 9-methyl-7-bromoeudistomin D (MBED) and the concomitant activation of large conductance Ca2+-dependent K+ (BK) channels were analyzed using confocal Ca2+ imaging and whole cell voltage-clamp methods in guinea pig urinary bladder smooth muscle cells. Puff application of 3 or 10 mM caffeine for several seconds (2 - 5 s) elicited a large increase in intracellular Ca2+ concentration ([Ca2+]i) and induced a phasic outward current at a holding potential of -40 mV. The phasic outward current was the summation of spontaneous transient outward currents (STOCs) due to marked activation of BK channels and was followed by a short cessation of STOCs. Although the increase in superficial [Ca2+]i by caffeine was faster than that in global [Ca2+]i, the peak [Ca2+]i was identical in these areas. Puff application of 100 microM MBED also markedly enhanced STOCs for a few seconds. This response to MBED was not observed when stored Ca2+ was depleted by caffeine. The increase in [Ca2+]i by MBED occurred mainly in superficial areas. Longer application of 100 microM MBED for 2 min did not induce significant global [Ca2+]i increase but decreased the amount of Ca2+ release and cell shortening during the subsequent application of 10 mM caffeine. These results indicate that short application of MBED releases Ca2+ preferentially from superficial storage sites, presumably due to its slow approach to deeper sites. MBED may be a good pharmacological tool to manipulate selectively the superficial Ca2+ stores related to STOCs.
Ohi
Y
Y
Department of Molecular and Cellular Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.
Atsuki
K
K
Tori
Y
Y
Ohizumi
Y
Y
Watanabe
M
M
Imaizumi
Y
Y
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002243:Carbolines / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D018613:Microscopy, Confocal; D009130:Muscle, Smooth / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D001743:Urinary Bladder / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
D002243:Carbolines; D010726:Phosphodiesterase Inhibitors; D015221:Potassium Channels; C060741:9-methyl-7-bromoeudistomin D; D002110:Caffeine; D002118:Calcium