Abstract

Hypocapnia produces cerebral vasoconstriction. The mechanisms involved in hypocapnia-induced elevation of vascular smooth muscle tone remain unclear. We addressed the hypothesis that, in cerebrovascular smooth muscle, increases in extracellular pH (pHo) cause increases in Ins(1,4,5)P3 and cytosolic calcium ([Ca2+]c). Superfused primary cultures of piglet cerebral microvascular smooth muscle cells were exposed to artificial CSF (aCSF) of control (pHo 7. 4, PCO2 36 mm Hg), metabolic alkalosis (pHo 7.7, PCO2 36 mm Hg), or respiratory alkalosis (pHo 7.7, PCO2 19 mm Hg). Intracellular pH (pHi) and [Ca2+]c were measured, using BCECF and fura-2, respectively, with dual wavelength spectroscopy. Ins(1,4,5)P3 was determined by a protein binding assay. Both metabolic and respiratory acidosis treatments increased pHi from the control value of about 7.2 to 7.35. Metabolic and respiratory alkalosis increased Ins(1,4,5)P3, as we showed previously. Metabolic and respiratory alkalosis increased [Ca2+]c about 80% and 110%, respectively. Neither Ins(1,4,5)P3 nor [Ca2+]c increased in cells treated with aCSF that produced control pHo with increased pHi (7.3). In contrast, when pHo increased (7.7), but pHi was maintained at control (7.2), Ins(1,4,5)P3 increased from 123 pmol/well to 307 pmol/well and [Ca2+]c increased 46%. However, the increase of [Ca2+]c was less than with either respiratory or metabolic alkalosis. Thus, hypocapnia-induced cerebral vasoconstriction could involve production of Ins(1,4,5)P3 with resultant elevation in [Ca2+]c. While the Ins(1,4,5)P3 signal appears to be dependent on an increase in extracellular pH, a role for intracellular pH cannot be completely excluded.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.