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Infection of Chlorella NC64A cells by PBCV-1 produces a rapid depolarization of the host probably by incorporation of a viral-encoded K+ channel (Kcv) into the host membrane. To examine the effect of an elevated conductance, we monitored the virus-stimulated efflux of K+ from the Chlorella cells. The results indicate that all 8 Chlorella viruses tested evoked a host specific K+ efflux with a concomitant decrease in the intracellular K+. This K+ efflux is partially reduced by blockers of the Kcv channel. Qualitatively these results support the hypothesis that depolarization and K+ efflux are at least partially mediated by Kcv. The virus-triggered K+ efflux occurs in the same time frame as host cell wall degradation and ejection of viral DNA. Therefore, it is reasonable to postulate that loss of K+ and associated water fluxes from the host lower the pressure barrier to aid ejection of DNA from the virus particles into the host.