Insulin-dependent rescue from cardiogenic shock is not mediated  by phospholamban phosphorylation.
BACKGROUND
We used immunoblots to determine whether inotropic and lusitropic effects of high-dose insulin (HDI) in cardiogenic shock, induced by a beta-blocker (BB) or a calcium channel blocker (CCB), are mediated by phosphorylation of phospholamban (PLB). PLB is a membrane protein that regulates calcium uptake into the sarcoplasmic reticulum (SR) by inhibition of the cardiac calcium pump (SERCA2a). Phosphorylation of PLB relieves SERCA inhibition, thus enhancing diastolic relaxation and preload.


METHODS
Our Institutional Animal Care and Use Committee approved this research. Swine myocardia from six groups were flash frozen immediately upon death or sacrifice. Groups 1-6 received: (1) no medications, (2) HDI and glucose only, (3) toxic propranolol infusions and saline resuscitation, (4) toxic propranolol infusions and HDI resuscitation, (5) toxic verapamil infusions and saline resuscitation, and (6) toxic verapamil infusions and HDI resuscitation. Groups 3-6 were resuscitated for 4 h. Tissue samples from all six groups were analyzed by quantitative immunoblots, using antibodies to both unphosphorylated PLB (uPLB) and phosphorylated PLB (pPLB), to determine the total PLB content and the fraction of PLB phosphorylated.


RESULTS
There were no differences in either pPLB or total PLB in cardiac tissue among any of the six groups. However, infusion of a pig with the beta-adrenergic agonist, isoproterenol, produced enhanced PLB phosphorylation.


CONCLUSIONS
The mechanism by which HDI produces its inotropic and lusitropic effects in CCB- and BB-induced cardiovascular toxicity, resulting in resuscitation, is not due to changes in phosphorylation of PLB or a change in the total PLB in the SR.
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55101, USA.
Naa-Adjeley
NA
Ablorh
Florentin
F
Nitu
Kristin
K
Engebretsen
David D
DD
Thomas
Joel S
JS
Holger
D000319:Adrenergic beta-Antagonists / Q000633:toxicity; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000633:toxicity; D002135:Calcium-Binding Proteins / Q000187:drug effects* / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D015151:Immunoblotting; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011433:Propranolol / Q000633:toxicity; D012151:Resuscitation / Q000379:methods; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D012770:Shock, Cardiogenic / Q000139:chemically induced / Q000188:drug therapy*; D013552:Swine; D014700:Verapamil / Q000633:toxicity; D000099211:Phospholamban
D000319:Adrenergic beta-Antagonists; D002118:Calcium; D002121:Calcium Channel Blockers; D002135:Calcium-Binding Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D011433:Propranolol; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D014700:Verapamil; D000099211:Phospholamban