Measurement of intracellular pH in isolated human detrusor smooth muscle cells

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

The effects of extracellular and intracellular pH on intracellular Ca2+ regulation in guinea-pig detrusor smooth muscle

1. Intracellular pH (pHi) and intracellular [Ca2+] ([Ca2+]i) were measured during changes to superfusate PCO2 and/or [NaHCO3]. Changes to superfusate PCO2 produced sustained changes to pHi and [Ca2+]i, while changes to [NaHCO3] altered only extracellular pH (pHo). 2. Carbachol or caffeine induced a transient rise of [Ca2+]i due to Ca2+ release from an intracellular store. This Ca2+ transient was reduced by extracellular acidosis, but increased by intracellular acidosis. Alkalosis in either compartment produced opposite effects to acidosis. Changes to the Ca2+ transient mirrored those to phasic tension previously reported in this preparation. 3. A raised superfusate [K+] also induced a Ca2+ transient, due to transmembrane influx of Ca2+. This transient was depressed by extracellular acidosis, but unaffected by changes to pHi. The L-type Ca2+ current was similarly affected by changes to pHo, but not by alteration of pHi. 4. The results suggest that extracellular acidosis depresses the Ca2+ transient by reducing transmembrane influx through the L-type Ca2+ channel. The increase in the carbachol- and caffeine-induced Ca2+ transients by intracellular acidosis is due to enhancement of Ca2+ uptake into intracellular stores as a result of a raised resting [Ca2+]i.