title: Protein kinase A regulation of T-type Ca2+ channels in rat cerebral arterial smooth muscle.
abstract: Recent investigations have identified that T-type Ca(2+) channels (CaV3.x) are expressed in rat cerebral arterial smooth muscle. In the study reported here, we isolated the T-type conductance, differentiated the current into the CaV3.1/CaV3.2 subtypes and determined whether they are subject to protein kinase regulation. Using patch clamp electrophysiology, whole-cell Ba(2+) current was monitored and initially subdivided into nifedipine-sensitive and -insensitive components. The latter conductance was abolished by T-type Ca(2+) channel blockers and was faster with leftward shifted activation/inactivation properties, reminiscent of a T-type channel. Approximately 60% of this T-type conductance was blocked by 50 µM Ni(2+), a concentration that selectively interferes with CaV3.2 channels. Subsequent work revealed that the whole-cell T-type conductance was subject to protein kinase A (PKA) modulation. Specifically, positive PKA modulators (db-cAMP, forskolin, isoproterenol) suppressed T-type currents and evoked a hyperpolarized shift in steady-state inactivation. Blocking PKA (with KT5720) masked this suppression without altering the basal T-type conductance. A similar effect was observed with stHt31, a peptide inhibitor of A-kinase anchoring proteins. A final set of experiments revealed that PKA-induced suppression targeted the CaV3.2 subtype. In summary, this study revealed that a T-type Ca(2+) channel conductance can be isolated in arterial smooth muscle, and differentiated into CaV3.1 and CaV3.2 components. It also showed that vasodilatory signaling cascades inhibit this conductance by targeting CaV3.2. Such targeting would impact Ca(2+) dynamics and consequent tone regulation in the cerebral circulation.
authors.affiliation: Hotchkiss Brain and Libin Cardiovascular Research Institutes and Department of Physiology and Pharmacology, University of Calgary, AB, T2N 4N1, Canada.
authors.forename: Osama F
authors.initials: OF
authors.lastname: Harraz
authors.forename: Donald G
authors.initials: DG
authors.lastname: Welsh
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism*; D002227:Carbazoles / Q000494:pharmacology; D002413:Cations, Divalent; D002536:Cerebral Arteries / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D007545:Isoproterenol / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011758:Pyrroles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
chemical_list: C500994:Cacna1g protein, rat; C509958:Cacna1h protein, rat; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D002227:Carbazoles; D002413:Cations, Divalent; D011758:Pyrroles; D005576:Colforsin; C057416:KT 5720; D009532:Nickel; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D009543:Nifedipine; D007545:Isoproterenol
keywords: Ca2+ Regulation; PKA; Vascular smooth muscle cells; Voltage-gated Ca2+ channels