摘要：

A single-electrode voltage-clamp technique was employed on in vitro hippocampal slices to examine the current responsible for the slow afterhyperpolarization (AHP) in pyramidal . This was achieved by using conventional procedures to evoke an AHP in current clamp, followed rapidly by a switch into voltage clamp (hybrid clamp). The AHP current showed a dependence on K+, which was close to that predicted for a K+ current by the Nernst equation. The AHP current could be blocked by + or . Although the AHP current showed a requirement for voltage-dependent entry, the current did not show any clear intrinsic voltage dependence. Once activated, AHP current is not turned off by hyperpolarizing the potential. The effects of , +, and (TEA) were used to identify an AHP current component to the outward current evoked by depolarizing voltage commands from holding potentials that approximate to the resting potential for these . The AHP current can contribute significantly to the outward current during the depolarizing command. Upon repolarization it is evident as a slow outward tail current. This slow tail current had the same time constant as AHP currents evoked by hybrid clamp. Fast components to the tail currents were also observed. These were sensitive to + and TEA. They probably represent a voltage-sensitive gKCa, sometimes termed C-current. The strong sensitivity to voltage and TEA displayed by the conventionally described gKCa (IC) are properties inconsistent with the AHP. It seems likely that the AHP current (IAHP) represents a -activated K+ current separate from IC and that these two currents coexist in the same .

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