Reduced calcium responsiveness characterizes contractile dysfunction following coronary microembolization

We addressed calcium responsiveness in microembolized myocardium at 6 h after coronary microembolization (ME). Methods and results In anesthetized pigs calcium responsiveness was determined as the increase of a myocardial work index (WI; LV pressure development vs. wall thickening) in response to a graded intracoronary infusion of CaCl2 at baseline and at 6 h after ME or placebo, respectively. At baseline, CaCl2 infusion increased WI in both groups (ME: 296 +/- 22 to 468 +/- 47 mmHg*mm; placebo: 324 +/- 24 to 485 +/- 38 mmHg*mm; mean +/- SEM). At 6 h after ME, WI was decreased by 159 +/- 16 mmHg*mm (P < 0.05 vs. baseline) and remained reduced at any calcium concentration, whereas it was unchanged with placebo. The calcium concentration in coronary blood necessary to achieve the half maximal increase in WI remained unchanged from baseline to 6 h and did not differ between placebo and ME. Conclusion The ME-induced myocardial dysfunction is not related to an altered calcium sensitivity, but is characterized by a reduced maximal contractile force.