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K+‐depolarization of efferent arterioles of juxtamedullary nephrons: A method for studies on Ca2+ entry and mobilization
Author(s) -
Feng MingGuo,
Navar L. Gabriel
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.761.18
Subject(s) - ryanodine receptor , vasoconstriction , chemistry , depolarization , vascular smooth muscle , biophysics , efferent , extracellular , intracellular , medicine , endocrinology , afferent , biochemistry , biology , smooth muscle
Increases in [Ca 2+ ] i involve Ca 2+ entry and mobilization mechanisms. We developed a method for studies on Ca 2+ mobilization from intracellular stores and entry from the extracellular space. Videomicroscopic measurements of vascular dimensions were performed on the rat isolated blood‐perfused juxtamedullary nephron preparation. Single efferent arterioles (EA) which get out of glomerulus, branch to form the descending vasa recta were selected for study. We used KCl‐induced K + ‐depolarization, an experimental means of activating voltage‐ activated L‐type Ca 2+ channels (LCC), to exclude the possibility of the action of LCC. We found that, in contrast to afferent arterioles, superfusion with KCl (55mM) caused only a slight constriction in EA indicating a weak activity of LCC in EA. Ryanodine, a modulator of intracellular ryanodine receptor(RyR)‐induced Ca 2+ release, caused constriction at low concentration (1μM) and dilation at high concentration (51μM) in K+‐depolarized EA indicating that ryanodine modulate Ca 2+ release from intracellular stores via RyR. Adding NE (1μM) to the high KCl treated EA elicited strong constriction. NE‐induced vasoconstriction was markedly inhibited by pretreatment with 2‐APB (100μM), a store‐operated channel (SOC), as well as IP 3 receptor blocker. However, ryanodine (51μM) failed to inhibit the NE‐induced vasoconstriction indicating that α 1 ‐adrenergic vasoconstriction predominantly involves IP3 dependant SOC activation, rather than LCC or RyR activation in EA. Our results are consistent with the previous observations obtained using other methods. This study provides a new, simple and effective method to investigate the mechanisms of Ca 2+ entry and mobilization. (supported by NHLBI HL‐18426)