Alkaline pH shifts Ca2+ sparks to Ca2+ waves in smooth muscle cells of pressurized cerebral arteries.
The effects of external pH (7.0-8.0) on intracellular Ca(2+) signals (Ca(2+) sparks and Ca(2+) waves) were examined in smooth muscle cells from intact pressurized arteries from rats. Elevating the external pH from 7.4 to 7.5 increased the frequency of local, Ca(2+) transients, or "Ca(2+) sparks," and, at pH 7.6, significantly increased the frequency of Ca(2+) waves. Alkaline pH-induced Ca(2+) waves were inhibited by blocking Ca(2+) release from ryanodine receptors but were not prevented by inhibitors of voltage-dependent Ca(2+) channels, phospholipase C, or inositol 1,4,5-trisphosphate receptors. Activating ryanodine receptors with caffeine (5 mM) at pH 7.4 also induced repetitive Ca(2+) waves. Alkalization from pH 7.4 to pH 7.8-8.0 induced a rapid and large vasoconstriction. Approximately 82% of the alkaline pH-induced vasoconstriction was reversed by inhibitors of voltage-dependent Ca(2+) channels. The remaining constriction was reversed by inhibition of ryanodine receptors. These findings indicate that alkaline pH-induced Ca(2+) waves originate from ryanodine receptors and make a minor, direct contribution to alkaline pH-induced vasoconstriction.
Heppner
Thomas J
TJ
Department of Pharmacology, University of Vermont College of Medicine, Burlington 05405-0068, USA.
Bonev
Adrian D
AD
Santana
L Fernando
LF
Nelson
Mark T
MT
D000468:Alkalies / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002536:Cerebral Arteries / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D066298:In Vitro Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
D000468:Alkalies; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D002118:Calcium