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Smooth Muscle Group, Department of Physiology, The Queen's University of Belfast, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK
The whole-cell perforated patch clamp technique was used to study membrane currents in isolated rabbit corpus cavernosum smooth muscle cells. Depolarization from –80 mV to the range –40 to –10 mV evoked a nifedipine-sensitive Ca2+ current that was followed by a slower inward current that activated over several hundred milliseconds. The slow current reversed near the Cl– equilibrium potential (ECl) and was reduced by anthracene-9-carboxylic acid (A9C; 1 mM) and niflumic acid (100 µM), suggesting that it was a Ca2+-activated Cl– current. When held constantly at –60 mV, over 70% of cells fired spontaneous transient inward currents (STICs), the amplitudes of which were reduced by A9C and niflumic acid. STICs reversed near ECl in a symmetrical Cl– gradient and when [Cl–]o was substituted with glutamate or I–, the reversal potential shifted to more positive or more negative values, respectively, confirming that STICs were mediated by Cl– channels. STICS were also blocked by cyclopiazonic acid, 2-aminoethoxydiphenyl borate (2-APB) and 2-nitro-4-carboxyl-N,N-diphenylcarbamate (NCDC), suggesting that they depended on IP3-mediated Ca2+-release from the sarcoplasmic reticulum. Modulation by the NO–cGMP pathway was investigated by applying nitrosocysteine, 3-(5-hydroxymethyl-2-furyl)-1-benzyl indazole (YC-1), and 8-bromo cGMP, all three of which abolished STIC activity. YC-1 also reduced noradrenaline-evoked inward currents, but had no effect on similar currents evoked by caffeine, suggesting that cGMP selectively inhibited IP3-mediated Ca2+ release. We propose that Ca2+-activated Cl– currents underlie detumescent tone in the corpus cavernosum, and that modulation of this mechanism by the NO–cGMP pathway is important during penile erection.
(Received 25 November 2003;
accepted after revision 3 February 2004;
first published online 6 February 2004)
Corresponding author K. D. Thornbury: Smooth Muscle Group, Department of Physiology, The Queen's University of Belfast, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK. Email: k.thornbury{at}qub.ac.uk
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