Different effects of azole-antifungal agents on the regulation of intracellular calcium concentration of Trichophyton rubrum.
Prior studies have indicated that intracellular calcium concentration ([Ca2+]i) is involved in fungal cell growth. However, it has not been known whether antifungal drugs affect signal transduction via calcium in fungal cells. In this context, we examined the effects of antifungal drugs, itraconazole, bifonazole and ketoconazole, on [Ca2+]i in Trichophyton rubrum. Itraconazole (1-5 ng/ml) induced a rapid and transient [Ca2+]i increase, peaking at 15-20s in hyphal cells of T. rubrum, but not in spores. The slow descending phase of the [Ca2+]i increase induced by itraconazole was depleted by chelating extracellular calcium with ethylene glycol bis (beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA), suggesting that the increase in [Ca2+]i is biphasic: Ca2+ mobilization from the internal pool and influx from the outside of the cell. At 10 ng/ml and 100 ng/ml, however, itraconazole induced an explosive and sustained calcium increase in both spores and hyphae. At less than 1 ng/ml, no [Ca2+]i increase was caused in both hyphae and spores. On the other hand, although some hyphal cells showed a transient [Ca2+]i increase, most of the cells did not show any changes of [Ca2+]i after the addition of ketoconazole at 10 ng/ml. Both spores and hyphal cells incubated with 100 ng/ml of bifonazole or ketoconazole showed a gradual increase of intracellular calcium concentration until 5 min, when the measurement was ceased. These findings suggest that signal transduction via calcium might be involved in some biological effects of itraconazole on T. rubrum, and that bifonazole and ketoconazole could differently affect [Ca2+]i in T. rubrum from itraconazole. In addition, the determination of [Ca2+]i changes induced by antifungal agents may contribute to clarification of the biological effects on fungal membranes.