DEPENDENCE OF CARDIAC CELL CA2-CONTAINING SARCOLEMMAL GANGLIOSIDES( PERMEABILITY ON SIALIC ACID)

The specific removal of negatively-charged sialic acid by neuraminidas e produces a large increase in cardiac myocyte Ca uptake (17.3+/-1.1 m mol Ca/kg dry weight) and marked cell contracture, Importantly, the in sertion of the negatively-charged amphiphile dodecyl sulfate in the sa rcolemma eliminates the increased calcium uptake and preserves contrac tile function. In the present study, we further examine the role of si alic acid-Ca interaction and, specifically, the role of gangliosides ( sialic acid-containing glycolipids) in cardiac cells' Ca permeability. Neonatal cell culture and adult ventricular myocytes were used, The m ajor findings of this study are: (1) while dodecyl sulfate inhibits ce llular calcium uptake and contracture development induced by sialic ac id removal, cationic and neutral amphiphiles are without effect, (2) C a channel blockers (nifedipine and protamine) and the Na/Ca exchange i nhibitor Ni do not modify the effect of sialic acid removal, (3) A non -classical-channel related whole-cell current appears and increases af ter 21 +/- 2.2 min treatment with 0.02 U/ml neuraminidase (n=4). Incub ation with neuraminidase in the presence of dodecyl sulfate greatly de lays the appearance of these currents to 44.4 +/- 6.1 min (n=4). (4) T he use of a specific probe for GM1 ganglioside, the cholera toxin B su bunit (3 mu g/ ml), induces a moderate but clear increase in cellular Ca (1.63 +/- 0.3 mmol Ca kg dry weight; n=8), However, this increase w as not modified by treatment with dodecyl sulfate, (5) Finally, 50 mU/ ml endoglycoceramidase, an enzyme which specifically cleaves the link between the sialic acid-containing oligosaccharide and ceramide of gan gliosides, induced a significant increase in Ca uptake (4.4+/-0.9 mmol Ca kg dry weight, n=4), These results indicate the importance of nega tively charged sialic acid-containing gangliosides in the maintenance of cardiac cell physiological Ca permeability. The increase in Ca upta ke induced by the removal of sialic acid seems to be mediated by devel opment of a Ca ''leak'' via other than classical cation channels, (C) 1998 Academic Press Limited.