ISSN:
1432-1424
Keywords:
surface charge
;
sialic acid
;
sinoatrial node
;
neuraminidase
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The whole-cell configuration of the patch-clamp technique was used with cultured pacemaker cells from the rabbit sinoatrial node to test the hypothesis that sialic acid residues (NANA) constitute much of the negative surface charge associated with hyperpolarization-activated, inward rectifying channels. Activation-voltage relationships (between −70 and −140 mV) were determined for hyperpolarization-activated (inward rectifying) current (i f). Addition of 10mm Ca2+ shifted the half-activation potential (V 1/2) from −89.5±0.9 mV to −77.9±2.6 mV (P〈0.01), confirming the presence of negative fixed charges on the myocytes after 3 to 5 days in culture. Addition of 20mm dimethonium, an organic divalent cation that “screens” but does not bind to negative surface charge, shiftedV 1/2 from −86.8±1.4 mV to −75.0±1.7 mV (P〈0.001) without affecting the amplitude of the current. In contrast, 10mm Ca2+ reduced the amplitude ofi f significantly. Incubation of cells with a highly purified preparation of neuraminidase (0.1–2.0 U/ml, 1 hr, 37°C), an enzyme that selectively removes NANA from glycoproteins and glycolipids, failed to alterV 1/2 or the amplitude ofi f significantly. Pretreatment of cells with neuraminidase (1.0 U/ml, 1 hr, 37°C) failed to alter the positive shift ofV 1/2 produced by dimethonium. The results suggest that NANA does not constitute the negative surface charge associated with hyperpolarization-activated, inward rectifying channels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869385
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