Higher Expression of TRPM7 Channels in Murine Mature B Lymphocytes than Immature Cells

TRPM7, a cation channel protein permeable to various metal ions such as Mg2+, is ubiquitously expressed in variety of cells including lymphocytes. The activity of TRPM7 is tightly regulated by intracellular Mg2+, thus named Mg2+-inhibited cation (MIC) current, and its expression is known to be critical for the viability and proliferation of B lymphocytes. In this study, the level of MIC current was compared between immature (WEHI-231) and mature (Bal-17) B lymphocytes. In both cell types, an intracellular dialysis with Mg2+-free solution (140 mM CsCl) induced an outwardly-rectifying MIC current. The peak amplitude of MIC current and the permeability to divalent cation (Mn2+) were several fold higher in Bal-17 than WEHI-231. Also, the level of mRNAs for TRPM7, a molecular correspondence of the MIC channel, was significantly higher in Bal-17 cells. The amplitude of MIC was further increased, and the relation between current and voltage became linear under divalent cation-free conditions, demonstrating typical properties of the TRPM7. The stimulation of B cell receptors (BCR) by ligation with antibodies did not change the amplitude of MIC current. Also, increase of extracellular [Mg2+]c to enhance the Mg2+ influx did not affect the BCR ligation-induced death of WEHI-231 cells. Although the level of TRPM7 was not directly related with the cell death of immature B cells, the remarkable difference of TRPM7 might indicate a fundamental change in the permeability to divalent cations during the development of B cells.

M3 Subtype of Muscarinic Receptors Mediate Ca2+ Release from Intracellular Stores in Rat Prostate Neuroendocrine Cells

Our previous studies document the expression of adrenoceptors and purinoceptors in the rat prostate neuroendocrine cells (RPNECs). However, a direct investigation of the receptors for acetylcholine (ACh) is still lacking in the prostate neuroendocrine cells. RPNECs were freshly isolated from the ventral lobes of rat prostate by using collagenase. Effects of ACh and various muscarinic antagonists on the intracellular Ca2+ concentration ([Ca2+]c ) were investigated by using the fura-2 spectrofluorimetry. Single-cell RT-PCR analysis was applied to identify the transcripts for the muscarinic receptor subtypes. ACh (5 micrometer) induced a sharp transient increase in the [Ca2+]c of RPNECs, which was independent of the extracellular Ca2+. In the same RPNECs, high KCl (60 mM), phenylephrine (5micrometer), UTP (P2Y1/2 agonist, 50, micrometer), and alpha, beta-meATP (P2X1/3 agonist, 0.5micrometer) also increased the [Ca2+]c. The ACh-induced [Ca2+]c change (delta[Ca2+]c ) was blocked by atropine or by para-fluorohexahydrosiladifenidol (M3 antagonist, 0.3micrometer), but not by telenzepine (M1 antagonist, 1 micrometer) and himbacine (M2 and M4 antagonist, 1 mircoM). The single-cell RT-PCR demonstrated the selective expression of mRNAs for M3 in RPNECs. In summary, RPNECs express M3 muscarinic receptors that are linked to the release of Ca2+ from intracellular stores. The Ca2+ signals of RPNECs might mediate the parasympathetic regulation of prostate gland.