A new PTEN opener or a new opener of a large conductance Ca2+-activated K+ channel (Maxi-K channel) which comprises as an active ingredient a tetrazolylalkoxy-dihydrocarbostyril compound of the formula (I): wherein R is cycloalkyl, A is lower alkylene, and the bond between 3- and 4-positions of the carbostyril nucleus is single bond or double bond, or a salt thereof, which is useful as a medicament for promotion of the survival of normal cells, brain cells, heart cells, and skin, and further for inhibiting of Gram negative sepsis and cell migration and cell invasion due to inhibition of PTEN and is further useful as a medicament for the treatment of neuronal disorders, for example, an anticonvulsant, a neuroprotecting agent, a medicament for treatment of regional cerebral edema and neurologic motor impairment, cognitive disorders, traumatic brain injury, Parkinson's disease, epilepsy, migraine, and Alzheimer's disease, etc.