L‐type calcium channel expression depends on the differentiated state of vascular smooth muscle cells

Abstract

Despite intensive interest in understanding the differentiation of vascular smooth muscle cells (VSMC), no information is available about differential regulation of ion channels in these cells. Since expression of the L-type Ca2+ channel can be influenced by differentiation in other cell types, we tested the hypothesis that the L-type (C class) channel is a specific differentiation marker of VSMC and that expression of these channels depends on the state of cell differentiation. We used rat aortic (A7r5) VSMC, which express functional L-type Ca2+ channels, and induced dedifferentiation by cell culture in different media. Treatment with retinoic acid was used to redifferentiate the VSMC. We characterized the differentiated state of the cells by using immunohistochemistry and Western blot analysis for smooth muscle (SM) alpha-actin and SM-myosin heavy chain (MHC). The number of functional Ca2+ channels was significantly decreased in dedifferentiated VSMC and increased upon differentiation with retinoic acid. Ca2+ channel function was assessed by whole-cell voltage clamp techniques. Using Western blot and dihydropyridine binding analysis, we found that the expression of the Ca2+ channel alpha1 subunit, and to a lesser extent the beta2 subunit, was directly correlated with the expression of SM alpha-actin and SM-MHC. We conclude that expression of L-type Ca2+ channel alpha1 subunits, and thus a functional Ca2+ channel, is highly coordinated with expression of the SM-specific proteins required for specialized smooth muscle cell functions. Furthermore, our results demonstrate that the L-type Ca2+ channel is a novel marker for differentiation of VSMC. The data suggest that regulation of ion channel expression during differentiation may have physiological importance for normal smooth muscle function and may influence VSMC behavior under pathophysiological conditions.

Intracellular Ca 2+ Handling in Vascular Smooth Muscle Cells Is Affected by Proliferation

“…Changes in the expression of the voltage-dependent Ca 2ϩ channels were also recently reported. 5,6 We demonstrate that alteration in the expression of the proteins involved in intracellular Ca 2ϩ handling is also part of this process: proliferation is associated with loss of SERCA2a and RyR3. Only SERCA2b and IP3R are present, at RNA and protein levels, in proliferating cells.…”

“…Voltagegated Ca 2ϩ currents also vary. [3][4][5] Freshly dissociated rat aortic smooth muscle cells (RASMCs) have functional L-and T-type Ca 2ϩ channels, but when they proliferate, the proportion of the L-type channels decreases, whereas that of the T-type channels increases. The changes are dependent on the cell cycle.…”

“…6 Furthermore, alteration in expression of the ␣ 1 , ␤ 2 , and ␤ 3 subunits of the L-type Ca 2ϩ channel was recently reported in culture. 5 Changes in the response to caffeine, ryanodine, and angiotensin II have been reported during vascular smooth muscle cell culture. [7][8][9] This suggests modifications in the intracellular Ca 2ϩ stores, but the molecular events underlying these pharmacological properties are unknown.…”

In Vitro And In Vivo Activation of Rat Hepatic Stellate Cells Results In De Novo Expression of L–Type Voltage–Operated Calcium Channels

“…6,30 It is well known that intracellular Ca 2ϩ , besides playing a role in cell contraction, is also involved in a number of cell functions, such as differentiation, proliferation, migration, apoptosis, and protein synthesis. [31][32][33] The up-regulation of VOCC in HSCs could, therefore, have other pathophysiologic implications. First, it could be speculated that the expression of VOCC rather than being one of the consequences of cell activation is an essential step in the process of phenotypic transition into myofibroblast-like cells.…”

A small-conductance Ca2+-activated K+ current and Cl- current in rat dental pulp cells.

“…Therefore, it would be interesting to relate actions of these sensory neuropeptides and chemical mediators to the modulation of K ‫ם‬ and Cl ‫מ‬ conductances in dental pulp cells. As described in a wide variety of cells, ion channels can be involved in the signal codes for proliferation, secretion of extracellular matrix proteins and cell differentiation 8,11,20,22) as well as the intercellular electrical/chemical communications through gap junctions 2,3,8,9,19,21,24,28) . The K ‫ם‬ and Cl ‫מ‬ channels expressed in dental pulp cells are most likely responsible for cellular functions underlying dental pulp metabolisms.…”