In this paper we propose a cluster-based multichannel scheduling algorithm for intra-cluster communications in Cognitive Radio Sensor Networks (CRSNs) to avoid collisions between neighbor clusters. Since nodes having neighbor nodes out of their clusters may cause collisions between neighbor clusters, when transmitting in the same time slot on the same channel, the scheduling of each cluster cannot be established independently. We propose to fix in each cluster the channels used by nodes having conflicting nodes out of their clusters. This channel assignment is done by the cluster heads in a distributed way but according to the decreasing priority order of the clusters. Then, each cluster head executes the scheduling algorithm independently. We evaluate the performance of this algorithm in terms of total number of time slots needed by all the nodes to transmit all their packets to the sink, energy consumption and transmission time interval.