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This Article Full Text Full Text (PDF) All Versions of this Article: 294/1/H285    most recent 00824.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tsujikawa, H. Articles by Okada, T. Search for Related Content PubMed PubMed Citation Articles by Tsujikawa, H. Articles by Okada, T.

Cholesterol depletion modulates basal L-type Ca²⁺ current and abolishes its β-adrenergic enhancement in ventricular myocytes

¹Department of Physiology, Juntendo University School of Medicine, Tokyo, Japan; and ²Department of Physiology, New York Medical College, Valhalla, New York

Submitted 16 July 2007 ; accepted in final form 29 October 2007

Cholesterol is a primary constituent of the plasmalemma, including the lipid rafts/caveolae, where various G protein-coupled receptors colocalize with signaling proteins and channels. By manipulating cholesterol in rabbit and rat ventricular myocytes using methyl-β-cyclodextrin (MβCD), we studied the role of cholesterol in the modulation of L-type Ca²⁺ currents (I_Ca,L). MβCD was mainly dialyzed from BAPTA-containing pipette solution during whole cell clamp. In rabbit myocytes dialyzed with 30 mM MβCD for 10 min, a positive shift in membrane potential at half-maximal activation (V_0.5) from –8 to –2 mV developed and was associated with an increase in current density at positive potentials (42% at +20 mV vs. time-matched controls). Isoproterenol (ISO) increased I_Ca,L approximately threefold and caused a negative shift in V_0.5 in control cells, but it did not increase I_Ca,L in MβCD-treated myocytes, nor did it shift V_0.5. The effect of MβCD (10 or 30 mM) was concentration dependent: 30 mM MβCD suppressed the ISO-induced increase in I_Ca,L more effectively than 10 mM MβCD. MβCD dialysis also abolished the increase in I_Ca,L elicited by forskolin or dibutyryl cAMP, but not that elicited by (–)BAY K 8644. External application of MβCD-cholesterol complex to rat myocytes attenuated the MβCD-mediated inhibition of the ISO-induced increase of I_Ca,L. Biochemical analysis confirmed that the myocytes' cholesterol content was diminished by MβCD and increased by MβCD-cholesterol complex. Cholesterol thus appears to contribute to the regulation of basal I_Ca,L and β-adrenergic cAMP/PKA-mediated increases in I_Ca,L. We suggest that cholesterol affects the structural coupling between L-type Ca²⁺ channels and adjacent regulatory proteins.

lipid raft; adenosine 3',5'-cyclic monophosphate; protein kinase A; phosphorylation