Modulation of ouabain-insensitive Na(+)-ATPase activity in the renal proximal tubule by Mg(2+), MgATP and furosemide.

In addition to the (Na(+)+K(+))ATPase another P-ATPase, the ouabain-insensitive Na(+)-ATPase has been observed in several tissues. In the present paper, the effects of ligands, such as Mg(2+), MgATP and furosemide on the Na(+)-ATPase and its modulation by pH were studied in the proximal renal tubule of pig. The principal kinetics parameters of the Na(+)-ATPase at pH 7.0 are: (a) K(0.5) for Na(+)=8.9+/-2.2mM; (b) K(0.5) for MgATP=1.8+/-0.4mM; (c) two sites for free Mg(2+): one stimulatory (K(0.5)=0.20+/-0.06 mM) and other inhibitory (I(0.5)=1.1+/-0.4 mM); and (d) I(0.5) for furosemide=1.1+/-0.2 mM. Acidification of the reaction medium to pH 6.2 decreases the apparent affinity for Na(+) (K(0.5)=19.5+/-0.4) and MgATP (K(0.5)=3.4+/-0.3 mM) but increases the apparent affinity for furosemide (0.18+/-0.02 mM) and Mg(2+) (0.05+/-0.02 mM). Alkalization of the reaction medium to pH 7.8 decreases the apparent affinity for Na(+) (K(0.5)=18.7+/-1.5 mM) and furosemide (I(0.5)=3.04+/-0.57 mM) but does not change the apparent affinity to MgATP and Mg(2+). The data presented in this paper indicate that the modulation of the Na(+)-ATPase by pH is the result of different modifications in several steps of its catalytical cycle. Furthermore, they suggest that changes in the concentration of natural ligands such as Mg(2+) and MgATP complex may play an important role in the Na(+)-ATPase physiological regulatory mechanisms.

Vinblastine, actinomycin D, bleomycin, cyclophosphamide and cis-platinum for advanced germ cell testis tumors: Brazilian experience.

Disseminated germ cell testicular cancer proved to be highly sensitive to platinum-containing chemotherapy regimens. We present data concerning the treatment of advanced seminoma and nonseminomatous tumors in a developing country. We treated 30 patients with advanced germ cell testis tumors with 3 or 4 cycles of vinblastine, actinomycin D, bleomycin, cyclophosphamide and cis-platinum. Surgical resection of residual masses was done 30 days after completion of chemotherapy in 18 patients. The histology of the primary tumor was seminoma in 13 patients and nonseminomatous tumors in 17. Toxicity was mild and no treatment-related deaths occurred. All 13 patients (100 per cent) with seminoma and 12 of 17 patients (71 per cent) with nonseminomatous tumors had a complete response to chemotherapy, and 1 of 17 patients was free of disease after a debulking operation and additional chemotherapy. A total of 3 patients with seminoma and 2 with nonseminomatous tumors had recurrences 5 to 8 months after an initial complete response and received additional chemotherapy (VP-16 regimen) with or without radiotherapy. Complete clinical response was achieved in 4 of 5 patients. Median followup was 24 months (range 8 to 38 months) in the 13 patients with seminoma and 28 months (range 9 to 58 months) in those with nonseminomatous tumors, and 13 (100 per cent) and 12 (71 per cent), respectively, are alive without evidence of disease. These data suggest that the protocol of vinblastine, actinomycin D, bleomycin, cyclophosphamide and cis-platinum is highly effective and minimally toxic in the treatment of disseminated germ cell testicular cancer, inducing an 83 per cent long-lasting clinical remission. Seminomas seem to be equally or even more sensitive than nonseminomatous tumors to this platinum-containing chemotherapy regimen. Recurrence after initial complete response can be treated successfully with regimens containing VP-16.