Loose-patch clamp currents from the hypothalamo-neurohypophysial system of the rat

The loose-patch clamp technique was used to study voltage-activated currents from the surface of rat neurohypophysial and hypothalamic regions in situ. In the neurohypophysis, depolarizing pulses of 4-8 ms duration yielded tetrodotoxin (TTX)-sensitive sodium currents, a 4-AP-sensitive "A"-type potassium current, and a long-lasting outward TEA- and tetrandrine-sensitive Ca(2+)-activated potassium current. All of these currents were elicited during the application of the pulse. With high external calcium there were long-lasting inward currents blocked by Ni(2+) and Cd(2+), identifying them as voltage-gated calcium currents. Depolarizing pulses of 0.3-0.7 ms duration yielded fast biphasic responses, of 1-3 ms duration, composed of mostly sodium and "A"-type potassium currents. With high external calcium there were fast inward currents blocked by Ni(2+) and Cd(2+), indicating that these were voltage-gated calcium currents. These responses have the characteristics of action potential currents: they were elicited after the cessation of the applied pulse and the "A" component is eliminated together with the sodium component upon application of TTX. Similar responses to long and short pulses were obtained from the surface of the associated magnocellular somata in the supraoptic nucleus, and their projections. The explant currents are similar to those previously characterized using conventional methods from somata and terminals.