NUCLEAR-MEMBRANE RECEPTORS AND CHANNELS - POTENTIAL THERAPEUTIC TARGETS FOR DRUG-ACTION

The recent use of confocal microscopy showed for the first time that t he nucleus plays an important role! in excitation-contraction and secr etion coupling of several excitable and nonexcitable cells. It was als o suggested that, like the sarcolemma membrane, the nuclear membrane i ndeed possesses channels as well as receptors which could play a major role in modulating Ca2+ influx and cytosolic Ca2+ buffering capacity of the nucleus. In this study, the mechanism(s) of Ca2+ entry through the sarcolemma and the nuclear membrane during spontaneous contraction of heart cells and during sustained stimulation of ET-1 and Ang-II re ceptors were examined in cardiomyocytes as well as in human vascular s mooth muscle and endothelial cells. During spontaneous contraction of heart cells, the cytosolic Ca2+ increase was immediately followed by a transient increase of nuclear Ca2+, both of which were blocked by the L-type Ca2+ channel blocker apamine at a concentration of 100 nM. Sus tained stimulation of bradykinin, Ang-II, or ET-1 receptors induced a sustained increase of intracellular Ca2+ which was mainly nuclear. Usi ng the cell attached patch clamp configuration, the potent voltage-dep endent steady-state R-type Ca2+ channel blocker PN200-110 (in the pres ence of the specific L-type Ca2+-blocker nifedipine) decreased the PAF -induced increase of the probability of opening the sarcolemmal steady -state resting voltage-dependent R-type Ca2+ channel. The use of an An g-II fluorescent probe and sarcolemmal perforated technique showed tha t Ang II receptors are also located at the nuclear membrane level. The se results demonstrate that like the sarcolemmal membrane, the nuclear membrane possesses receptors as well as channels that could be a targ et for cytosolic free hormones, and thus also constituting a new targe t for drug action. (C) 1997 Wiley-Liss, Inc.