The object of this study was to characterise membrane currents in corpus cavernosum cells.
Male rabbits were killed with pentobarbitone (I.V.) and cells were freshly dispersed from the corpus cavernosum for study using the amphotericin B perforated patch technique. Patch pipettes contained caesium to block potassium currents. Cells were held at -60 mV and stepped to potentials of -80 mV to +50 mV.
Transient inward current was observed at the beginning of the test steps, typical of L-type calcium current. There was also a slowly developing current that was inward at negative potentials, reaching a maximum of -127 ± 19 pA (mean ± S.E.M., n = 19) at -20 mV. This current reversed between -10 and 0 mV, which was close to the chloride equilibrium potential of 0 mV, and became a large outward current at positive potentials (911 ± 85 pA at +50 mV, n = 19). In eight cells the chloride channel antagonist anthracene-9-carboxylic acid (9AC; 1 mM) reduced the slow inward current at -20 mV from -180 ± 57 to -41 ± 12 pA (P < 0.02, Student’s paired t test) and reduced the outward current at +50 mV from 871 ± 151 to 227 ± 41 pA (P < 0.01). Similarly, niflumic acid (100 µM) reduced the maximal inward and outward currents from -161 ± 44 to -86 ± 64 pA (P < 0.05, n = 6) and from 1141 ± 45 to 500 ± 82 pA (P < 0.01, n = 6), respectively. The slow inward current at -20 mV was also greatly reduced by nifedipine (10 µM) from -254 ± 98 to -19 ± 12 pA (P < 0.05, n = 4), as was the outward current at +50 mV from 1364 ± 354 to 135 ± 27 pA (P < 0.05, n = 4). These results suggest that the slow current was a Ca2+-activated Cl– current, similar to those previously described in the urethra (Cotton et al. 1997; Sergeant et al. 2000). More than 80 % of the corpus cells also generated spontaneous transient inward current (STICs) when held constant at -60 mV. The STICs were reduced in amplitude by 1 mM 9AC (from 146 ± 73 to 28 ± 15 pA, P < 0.01, n = 5) and by 100 µM niflumic acid (from 215 ± 85 to 108 ± 38 pA, P < 0.05, n = 5). The reversal potential of the STICs was measured by applying 200 ms ramp potentials from -50 to +50 mV. With 135 mM Cl– in the pipette and bath, the reversal potential was -1 ± 1 mV. This shifted to 20 ± 1 mV when external Cl– was reduced to 49 mM by replacement with glutamate (giving a calculated Cl– equilibrium potential of +27 mV) and to -19 ± 4 mV when all of the external Cl– was replaced with I–, suggesting that STICs were mediated by Cl– channels.
In conclusion, we have identified a calcium-activated chloride current in corpus cavernosum cells. Since it is likely to have a depolarizing effect under physiological conditions, we speculate that this current causes tone in these cells and therefore contributes to the detumescent state.
M.C. was supported by a DEL research studentship