Nuclear membrane receptors and channels: Potential therapeutical targets for drug action

Abstract

The recent use of confocal microscopy showed for the first time that the nucleus plays an important role in excitation‐contraction and secretion coupling of several excitable and nonexcitable cells. It was also suggested that, like the sarcolemma membrane, the nuclear membrane indeed 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 receptors were examined in cardiomyocytes as well as in human vascular smooth 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. Sustained stimulation of bradykinin, Ang‐II, or ET‐1 receptors induced a sustained increase of intracellular Ca2+ which was mainly nuclear. Using the cell attached patch clamp configuration, the potent voltage‐dependent steady‐state R‐type Ca2+ channel blocker PN200‐110 (in the presence 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 Ang‐II fluorescent probe and sarcolemmal perforated technique showed that Ang II receptors are also located at the nuclear membrane level. These results demonstrate that like the sarcolemmal membrane, the nuclear membrane possesses receptors as well as channels that could be a target for cytosolic free hormones, and thus also constituting a new target for drug action. Drug Dev. Res. 42:211–222, 1997. © 1997 Wiley‐Liss, Inc.

Role of endothelin-1 receptors in the sarcolemma membrane and the nuclear membrane in the modulation of basal cytosolic and nuclear calcium levels in heart cells

“…These results are in accordance with previous reports using similar preparations [1][2][3]. The results also showed that, in non-working heart cells, influx through the sarcolemma membrane and buffering of cytosolic Ca# + by the nucleus [1][2][3]4,6], probably via stimulation of the steady-state R-type Ca# + channel [1][2][3][4][5][6].…”

“…In another series of experiments, we used our ET-1 fluorescent probe [2,3] in order to label ET-1 receptors in intact and sarcolemma-perforated single heart cells [2,3] ; Figures 6(A)-6(D) show typical examples. Extracellular superfusion of intact non-working heart cells with the ET-1 fluorescent probe (1 nM) showed labelling of the receptors at the sarcolemma membrane in a cluster fashion.…”

“…The labelling was not prevented by BQ123 or BQ788, but was prevented by pretreatment with nonlabelled ET-1 (results not shown). Permeabilization of the cell membrane with Triton X-100 or ionomycin, which permits application of ET-1 into the cytosol [2,3], showed labelling of ET-1 receptors at both the sarcolemma and nuclear envelope membranes ( Figure 6E). This labelling was prevented by pretreatment with non-labelled ET-1.…”

“…Growing evidence in the literature indicates that the nucleus plays an important role in excitation-contraction and excitation-secretion coupling in excitable and nonexcitable cells, including those of the heart [1][2][3] and vascular smooth muscle [2,3,5,6]. In addition, it has been shown that the cytosolic application of angiotensin II [7] or of endothelin-1 (ET-1) [6,8] induces an increase in the sustained basal nucleoplasmic free Ca# + concentration ([Ca# + ] n ) in vascular smooth muscle cells.…”

“…In addition, it has been shown that the cytosolic application of angiotensin II [7] or of endothelin-1 (ET-1) [6,8] induces an increase in the sustained basal nucleoplasmic free Ca# + concentration ([Ca# + ] n ) in vascular smooth muscle cells. Furthermore, growing evidence has shown that receptors such as those for angiotensin II [2,9], prostaglandin E # [10] and ET-1 [2][3][4]11,12] are present in nuclear membranes. We demonstrated recently in vascular smooth muscle cells the presence in nuclear envelope membranes of functional ET-1 receptors that are insensitive to the ET A and ET B receptor antagonists BQ123 and BQ788 respectively [6].…”