Glucagon (Glu) influences renal tubular function and growth, although the signal transduction of Glu in the kidney still remains obscure. Rabbit cortical tubules were transformed by the pSV-neo3 gene to make a homogeneous cell colony, which responded to vasopressin but not to parathyroid hormone. The [Ca2+]i of the cells at the 9-10th passages was measured by the fluorescence indicator, fura-2. The [Ca2+]i was increased by Glu (10(-8) M) or bradykinin (10(-8) M), between which heterologous desensitization was observed. The Glu range of 10(-14) to 10(-6) M) significantly increased [Ca2+]i, while cAMP was not produced at any dose of Glu. Since the ranges of doses were from physiological to pharmacological, two concentrations of 10(-13) and 10(-8) M were employed to investigate the mechanisms. Glu at 10(-13) M led to a sustained rise in [Ca2+]i, which was completely blocked by external EGTA (5 mM, Ca-free solution). Glu at 10(-8) M provided a similar level of peak and sustained rise in [Ca2+]i, the sustained phase of which was blunted in Ca-free solution. Inositol tri/tetra phosphates were significantly increased by 10(-8) M, but not by 10(-13) M Glu. These data suggest that [Ca2+]i elevation is a major component of Glu-induced second messengers in the physiological and pharmacological range of doses of Glu, and that there might be two classes of pathways leading to increase in [Ca2+]i in transformed rabbit cortical collecting tubule cells.