In isolated rat hepatocytes, noradrenaline (NA) 50 nM induced intracellular calcium ([Ca2+](c)) increase as (i) oscillations with each down-stroke of the spike reaching baseline, (ii) phasic increase with gradual decay, and (iii) phasic increase transforming into oscillations. At 25 nM and 50 nM, NA predominantly induced oscillatory increases; at 100 nM and 1 muM, phasic increases were predominant. Photodynamic action (30 s) with photosensitizer sulphonated aluminium phthalocyanine (SALPC, 5 muM) induced [Ca2+](c) increase as (i) no change, (ii) a single spike, or (iii) phasic increase. [Ca2+](c) oscillations induced by NA 50 nM were obliterated by photodynamic action (30 s), but when NA 200 nM, which normally induced plateau increases, was added to the now quiescent cells, [Ca2+](c) oscillations reemerged. These data indicate that photodynamic action could efficiently desensitize adrenergic receptors in hepatocytes. Photodynamic action may do so by crosslinking neighboring receptors or neighboring transmembrane domains of the same receptor.