Chick cardiomyocytes, when submitted to hyposmotic swelling, exhibit a partial regulatory volume decrease (RVD). A Ca 2+ influx by stretch-activated channels signals a taurine efflux and the RVD at 37 o C. We evaluated the cells performance at room temperature. Cardiomyocytes isolated and cultured from 11-day-old chick embryos were submitted to a hyposmotic solution (180 mOsm/kg H 2 O) at 37 o C and at room temperature (26 o C). Under these conditions we measured the changes in cell volume as well as the intracellular free Ca 2+ (using fura-2). During hyposmotic swelling, cells at 37 o C displayed a peak relative volume of 1.61 ± 0.03 and recovery to 1.22 ± 0.04 (N = 14), while cells at 26 o C presented a peak swell relative volume of 1.74 ± 0.06 and did not recover (1.59 ± 0.09, N = 9). Transient increases in intracellular Ca 2+ , which are characteristic of the normal RVD, were observed at both temperatures (29.1 ± 4.5% (N = 8) and 115.2 ± 42.8% (N = 5) increase at 37 o and 26 o C (P<0.05), respectively). A delay in the Ca 2+ transient increase was also observed when the cells were at 26 o C (109 ± 34 s compared to 38 ± 9 s at 37 o C, P<0.05). At room temperature the RVD does not occur because the calcium transient increase, which is an early event in the signaling of the RVD, is delayed. Also, free calcium is not cleared as in the 37 o C RVD. In the normal RVD the free calcium returns to baseline levels. The very high and persistent free calcium levels seen at room temperature can lead to unregulated enzyme activities and may promote irreversible injury and cell death.

The present study aimed to ascertain the cytotoxicity of pesticides commonly used in rice cultivation, through in vitro assays employing the ZF-L cell line. The in vitro analyses investigated three cellular targets (cell membrane integrity, mitochondrial activity and lysosomal stability) in cells exposed to concentrations of Roundup Transorb® (67.7 μg L(-1), 135.4 μg L(-1) and 270.8 μg L(-1)), Furadan 350 SC® (0.1 μg L(-1), 0.05 μg L(-1) and 0.02 μg L(-1)). We also tested these products in combination. We analyzed the defensive capacity of the cells by measuring the activity of xenobiotic extruder proteins, as well as the expression of these same proteins. Cytotoxic effects of both pesticides were observed individually, as well as with the mixture of both products; including an inhibitory effect on the activity of xenobiotic extrusion. When exposed to the insecticide Furadan, and also the mixture of Furadan and Roundup, there was an increase in the expression of P glycoproteins (P-gps). There was also a negative correlation with cytotoxicity, mainly exhibited by mitochondrial activity and lysosomal integrity, but also with respect to the activity of P-gps. We observed that concentrations below those allowed by law were toxic regarding all parameters tested in this study, with the exception of mitochondrial function. Taken together, our results suggest that toxicity may be due to the surfactants present in the commercial formulations.