Journal
CIRCULATION RESEARCH
Volume 93, Issue 4, Pages 364-371Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1161/01.RES.0000086986.35568.63
Keywords
beta-adrenergic receptors; muscarinic receptors; calcium channels; knockout; adenylyl cyclase isoforms
Funding
- NHLBI NIH HHS [HL61476, HL65183, HL59729, HL65182, HL67724, HL69020, HL59139, HL33107] Funding Source: Medline
- NIA NIH HHS [AG14121] Funding Source: Medline
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In a genetically engineered mouse line with disruption of type 5 adenylyl cyclase (AC5(-/-)), a major cardiac isoform, there was no compensatory increase in other isoforms of AC in the heart. Both basal and isoproterenol (ISO)-stimulated AC activities were decreased by 30% to 40% in cardiac membranes. The reduced AC activity did not affect cardiac function (left ventricular ejection fraction [LVEF]) at baseline. However, increases in LVEF after ISO were significantly attenuated in AC5(-/-) (P<0.05, n=11). Paradoxically, conscious AC5(-/)- mice had a higher heart rate compared with wild-type (WT) mice (613±8 versus 523±11 bpm, P<0.01, n=14 to 15). Muscarinic agonists decreased AC activity, LVEF, and heart rate more in WT than in AC5(-/-). In addition, baroreflex-mediated, ie, neuronally regulated, bradycardia after phenylephrine was also attenuated in AC5(-/-). The carbachol-activated outward potassium current (at -40 mV) normalized to cell capacitance in AC5(-/-) (2.6+/-0.4 pA/pF, n=16) was similar to WT (2.9+/-0.3 pA/pF, n=27), but calcium (Ca2+)-mediated inhibition of AC activity and Ca2+ channel function were diminished in AC5(-/-). Thus, AC5(-/-) attenuates sympathetic responsiveness and also impairs parasympathetic and Ca2+-mediated regulation of the heart, indicating that those actions are not only regulated at the level of the receptor and G-protein but also at the level of type 5 AC.
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