Constitutive inhibitory G protein activity upon adenylyl cyclase-dependent cardiac contractility is limited to adenylyl cyclase type 6

TY - JOUR

T1 - Constitutive inhibitory G protein activity upon adenylyl cyclase-dependent cardiac contractility is limited to adenylyl cyclase type 6

AU - Bull Melsom, Caroline

AU - Cosson, Marie-Victoire

AU - Ørstavik, Øivind

AU - Lai, Ngai Chin

AU - Hammond, H Kirk

AU - Osnes, Jan-Bjørn

AU - Skomedal, Tor

AU - Nikolaev, Viacheslav

AU - Levy, Finn Olav

AU - Krobert, Kurt Allen

PY - 2019

Y1 - 2019

N2 - PURPOSE: We previously reported that inhibitory G protein (Gi) exerts intrinsic receptor-independent inhibitory activity upon adenylyl cyclase (AC) that regulates contractile force in rat ventricle. The two major subtypes of AC in the heart are AC5 and AC6. The aim of this study was to determine if this intrinsic Gi inhibition regulating contractile force is AC subtype selective.METHODS: Wild-type (WT), AC5 knockout (AC5KO) and AC6 knockout (AC6KO) mice were injected with pertussis toxin (PTX) to inactivate Gi or saline (control).Three days after injection, we evaluated the effect of simultaneous inhibition of phosphodiesterases (PDE) 3 and 4 with cilostamide and rolipram respectively upon in vivo and ex vivo left ventricular (LV) contractile function. Also, changes in the level of cAMP were measured in left ventricular homogenates and at the membrane surface in cardiomyocytes obtained from the same mouse strains expressing the cAMP sensor pmEPAC1 using fluorescence resonance energy transfer (FRET).RESULTS: Simultaneous PDE3 and PDE4 inhibition increased in vivo and ex vivo rate of LV contractility only in PTX-treated WT and AC5KO mice but not in saline-treated controls. Likewise, Simultaneous PDE3 and PDE4 inhibition elevated total cAMP levels in PTX-treated WT and AC5KO mice compared to saline-treated controls. In contrast, simultaneous PDE3 and PDE4 inhibition did not increase in vivo or ex vivo rate of LV contractility or cAMP levels in PTX-treated AC6KO mice compared to saline-treated controls. Using FRET analysis, an increase of cAMP level was detected at the membrane of cardiomyocytes after simultaneous PDE3 and PDE4 inhibition in WT and AC5KO but not AC6KO. These FRET data are consistent with the functional data indicating that AC6 activity and PTX inhibition of Gi is necessary for simultaneous inhibition of PDE3 and PDE4 to elicit an increase in contractility.CONCLUSIONS: Together, these data suggest that AC6 is tightly regulated by intrinsic receptor-independent Gi activity, thus providing a mechanism for maintaining low basal cAMP levels in the functional compartment that regulates contractility.

AB - PURPOSE: We previously reported that inhibitory G protein (Gi) exerts intrinsic receptor-independent inhibitory activity upon adenylyl cyclase (AC) that regulates contractile force in rat ventricle. The two major subtypes of AC in the heart are AC5 and AC6. The aim of this study was to determine if this intrinsic Gi inhibition regulating contractile force is AC subtype selective.METHODS: Wild-type (WT), AC5 knockout (AC5KO) and AC6 knockout (AC6KO) mice were injected with pertussis toxin (PTX) to inactivate Gi or saline (control).Three days after injection, we evaluated the effect of simultaneous inhibition of phosphodiesterases (PDE) 3 and 4 with cilostamide and rolipram respectively upon in vivo and ex vivo left ventricular (LV) contractile function. Also, changes in the level of cAMP were measured in left ventricular homogenates and at the membrane surface in cardiomyocytes obtained from the same mouse strains expressing the cAMP sensor pmEPAC1 using fluorescence resonance energy transfer (FRET).RESULTS: Simultaneous PDE3 and PDE4 inhibition increased in vivo and ex vivo rate of LV contractility only in PTX-treated WT and AC5KO mice but not in saline-treated controls. Likewise, Simultaneous PDE3 and PDE4 inhibition elevated total cAMP levels in PTX-treated WT and AC5KO mice compared to saline-treated controls. In contrast, simultaneous PDE3 and PDE4 inhibition did not increase in vivo or ex vivo rate of LV contractility or cAMP levels in PTX-treated AC6KO mice compared to saline-treated controls. Using FRET analysis, an increase of cAMP level was detected at the membrane of cardiomyocytes after simultaneous PDE3 and PDE4 inhibition in WT and AC5KO but not AC6KO. These FRET data are consistent with the functional data indicating that AC6 activity and PTX inhibition of Gi is necessary for simultaneous inhibition of PDE3 and PDE4 to elicit an increase in contractility.CONCLUSIONS: Together, these data suggest that AC6 is tightly regulated by intrinsic receptor-independent Gi activity, thus providing a mechanism for maintaining low basal cAMP levels in the functional compartment that regulates contractility.

KW - Adenylyl Cyclases/metabolism

KW - Animals

KW - Cell Membrane/drug effects

KW - Cyclic AMP/metabolism

KW - Cyclic Nucleotide Phosphodiesterases, Type 3/metabolism

KW - Cyclic Nucleotide Phosphodiesterases, Type 4/metabolism

KW - Female

KW - GTP-Binding Protein alpha Subunits, Gi-Go/metabolism

KW - Heart Ventricles/drug effects

KW - Male

KW - Mice, Inbred C57BL

KW - Mice, Knockout

KW - Myocardial Contraction/drug effects

KW - Myocardium/metabolism

KW - Pertussis Toxin/pharmacology

U2 - 10.1371/journal.pone.0218110

DO - 10.1371/journal.pone.0218110

M3 - SCORING: Journal article

C2 - 31173603

VL - 14

SP - e0218110

JO - PLOS ONE

JF - PLOS ONE

SN - 1932-6203

IS - 6

ER -