EPINEPHRINE AS A TOOL TO INVESTIGATE THE QUESTION OF RECYCLING OF SYMPATHETIC STORAGE-VESICLES IN THE HEART - CHEMICAL AND MORPHOLOGICAL-STUDIES

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 221  (3) , 820-827
Abstract
Reutilization of norepinephrine storage vesicles in the cardiac sympathetic nerves was studied. Studies were made to determine whether exocytotically depleted stores of norepinephrine could be restored by epinephrine and the restoration of epinephrine could be demonstrated by chemical and morphological examinations. Stimulation of guinea pig cardiac sympathetic nerves (1 Hz, 15 s/min for 75 min) in the presence of 20 mM tetraethylammonium lowered norepinephrine from 2.24 to 0.46 .mu.g/g. Exposure of such hearts to 6 or 60 .mu.M epinephrine increased epinephrine contents to 1.4 and 2.2 .mu.g/g, respectively. Accumulation of epinephrine by normal or norepinephrine-depleted heart was depressed over 90% by desipramine. If intermittent stimulation was given in the presence of tetraethylammonium for only 10 min, norepinephrine and epinephrine values of epinephrine-loaded hearts were reduced over 50%. Perfusion of such hearts with epinephrine-Krebs'' solution raised epinephrine content to 3.3 .mu.g/g. Stimulation-evoked overflows of epinephrine after 1st and 2nd loading with epinephrine were almost identical. Ca-free plus 1 mM ethylene glycol bis(.beta.-aminoethyl ether) N,N,N'',N''-tetraacetic acid completely blocked stimulation-evoked overflow of epinephrine. Dense-cored vesicles were observed in sympathetic nerves located in the region of the S-A [sino-atrial] node. Stimulation of nerves in the presence of tetraethylammonium resulted in almost complete disappearance of dense-cored vesicles. Perfusion of such treated hearts with epinephrine led to reappearance of dense-cored vesicles. The number of dense-cored vesicles after exposure to epinephrine was greater than that seen in the control tissue. Evidently storage vesicles are reused in sympathetic nerves of the guinea-pig heart.