title: Characterization of voltage operated R-type Ca2+ channels in modulating somatostatin receptor subtype 2- and 3-dependent inhibition of insulin secretion from INS-1 cells.
abstract: Somatostatin (SST) inhibits Ca(2+) entry into pancreatic B-cells via voltage-operated Ca(2+) channels (VOCCs) of L-type, leading to the suppression of insulin secretion. Activation of R-type channels increases insulin secretion. However, the role of R-type Ca(2+) channels (Ca(V)2.3) in mediating the effects of SST on insulin secretion has not been so far investigated. Here, we identify the SST-receptor subtypes (SSTR) expressed on insulin-producing INS-1 cells by RT-PCR and by functional assays. The role of R-type channels in regulating [Ca(2+)](i) in response to SST-treatment was detected by cell fluorescence imaging and patch-clamp technique. INS-1 expressed SSTR2 and SSTR3 and agonists (ag.) selective for these receptors reduced 10 nM exendin-4/20 mM glucose-stimulated insulin secretion. Surprisingly, SST and SST2-ag. transiently increased [Ca(2+)](i). Subsequently, these agonists led to a decrease in [Ca(2+)](i) below the basal levels. In contrast, SST3-ag. failed to induce a transient peak of [Ca(2+)](i). Instead, a persistent minor suppression of [Ca(2+)](i) was detected from 25 min. R-type channel blocker SNX-482 altered [Ca(2+)](i) in SST- and SST2-ag.-treated cells. Notably, the inhibition of insulin secretion by SST and SST2-ag., but not SST3-ag. was attenuated by SNX-482. Taken together, SST and SSTR2 regulate [Ca(2+)](i) and insulin secretion in INS-1 cells via R-type channels. In contrast, the R-type calcium channel does not mediate the effects of SST3-ag. on insulin secretion. We conclude that R-type channels play a major role in the inhibition of insulin secretion by somatostatin in INS-1 cells.
authors.affiliation: Augenklinik, Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, 13353 Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mergler
authors.forename: Vandana
authors.initials: V
authors.lastname: Singh
authors.forename: Carsten
authors.initials: C
authors.lastname: Grötzinger
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Kaczmarek
authors.forename: Bertram
authors.initials: B
authors.lastname: Wiedenmann
authors.forename: Mathias Z
authors.initials: MZ
authors.lastname: Strowski
mesh_terms: D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D020908:Calcium Channels, R-Type / Q000187:drug effects / Q000502:physiology*; D055724:Electrophysiological Phenomena; D007328:Insulin / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017481:Receptors, Somatostatin / Q000819:agonists / Q000378:metabolism*; D013004:Somatostatin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013111:Spider Venoms / Q000494:pharmacology; D013997:Time Factors
chemical_list: D020908:Calcium Channels, R-Type; D007328:Insulin; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; C115521:SNX 482; D013111:Spider Venoms; C103631:somatostatin receptor 3; D013004:Somatostatin; C093733:somatostatin receptor 2; D002118:Calcium