Na(+)/Ca(2+) exchange and its role in intracellular Ca(2+) regulation in guinea pig detrusor smooth muscle.
The role of Na(+)/Ca(2+) exchange in regulating intracellular Ca(2+) concentration ([Ca(2+)](i)) in isolated smooth muscle cells from the guinea pig urinary bladder was investigated. Incremental reduction of extracellular Na(+) concentration resulted in a graded rise of [Ca(2+)](i); 50-100 microM strophanthidin also increased [Ca(2+)](i). A small outward current accompanied the rise of [Ca(2+)](i) in low-Na(+) solutions (17.1 +/- 1.8 pA in 29.4 mM Na(+)). The quantity of Ca(2+) influx through the exchanger was estimated from the charge carried by the outward current and was approximately 30 times that which is necessary to account for the rise of [Ca(2+)](i), after correction was made for intracellular Ca(2+) buffering. Ca(2+) influx through the exchanger was able to load intracellular Ca(2+) stores. It is concluded that the level of resting [Ca(2+)](i) is not determined by the exchanger, and under resting conditions (membrane potential -50 to -60 mV), there is little net flux through the exchanger. However, a small rise of intracellular Na(+) concentration would be sufficient to generate significant net Ca(2+) influx.
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Department of Medicine, University College London, London W1P 7PN, United Kingdom.
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D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000187:drug effects / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013327:Strophanthidin / Q000494:pharmacology; D001743:Urinary Bladder / Q000166:cytology / Q000502:physiology
D019831:Sodium-Calcium Exchanger; D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium