TRANSIENT OUTWARD CURRENT IN ADULT-RAT SUPRAOPTIC NEURONS WITH SLICE PATCH-CLAMP TECHNIQUE - INHIBITION BY ANGIOTENSIN-II

1. Outward potassium currents were recorded from microscopically identified supraoptic neurones of adult Wistar male rats using the whole-cell patch-clamp technique in thin-slice preparations. The basic characteristics of transient outward current (I-A or A-current) and the effects of angiotensin II (AII) on the currents were studied. 2. I-A was isolated by subtracting outward currents elicited by stepping from two different holding potentials to a test potential or by applying 4-aminopyridine (4-AP) at 5 mM. The isolated I-A had a threshold for activation between -55 and -65 mV and was characterized by fast activation and inactivation. Values of the time to peak and the inactivation time constants for current decay at different test potentials were voltage dependent. 3. Normalized currents for activation and steady-state inactivation of I-A were fitted to the Boltzmann function. The mid-points and the slope factors were, respectively, -35.0 and -14.3 +/- 0.40 mV (n = 5) for the activation curve, and 72.0 and 7.0 +/- 0.68 mV (n = 5) for the inactivation curve. 4. The time course of recovery from inactivation was best fitted to a single exponential function with the time constant of 37.8 +/- 6.6 ms (n = 6). 5. The effects of AII on I-A and delayed rectifier current (I-K) were investigated. According to their responses to AII, cells were classified into two groups, sensitive and low-sensitive. Bolus injection of AII (10 mu M, 100 mu l) decreased the I-A amplitude by 25.1 +/- 2.4% in seven (53.8%) of the thirteen neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed by only 2.2 +/- 0.8%. Perfusion of AII (0.1 mu M) decreased the I-A amplitude by 21.3 +/- 3.1% in six (54.5%) of eleven neurones tested (sensitive group), whereas the other five neurones (low-sensitive group) changed only by 1.7 +/- 0.8%. Bolus injection of AII (10 mu M, 100 mu l) decreased the I-K amplitude 9.6 +/- 1.6% mV in five (45.5%) of the eleven neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed only by 0.46 +/- 0.27%. In the sensitive groups, the reduction of I-A by AII was significantly larger than that of I-K (P < 0.05). 6. Application of saralasin at 1 mu M, an AII antagonist, blocked the effects of AII on I-A. 7. These results suggest that the excitatory action of AII on supraoptic neurosecretory cells is mediated at least in part through suppression of I-A.