<apex:form >
    <apex:pageBlock >

        <apex:inputField value="{!Visit.Visit_date__c}" required="false" />
        <apex:pageBlockTable value="{!Participants}" var="u" title="Participants list" id="ParticipantsList">

            <apex:column headerValue="Participant Type" >
                <apex:inputField value="{!u.participant.RecordTypeId}"  >
                    <apex:actionSupport event="onchange" action="{!onRecordTypeChange}" reRender="ParticipantsList" >
                        <apex:param name="LineIndex" value="{!u.index}" assignTo="{!CurrentRow}" />
                    </apex:actionSupport>
                </apex:inputField>
            </apex:column>

            <apex:column headerValue="Participant" >
                <apex:inputField value="{!u.participant.User__c}" rendered="{!u.isInternal}" />
                <apex:inputField value="{!u.participant.Contact__c}" rendered="{!NOT(u.isInternal)}" />
            </apex:column>

            <apex:column headerValue="Index" >
                <apex:outputText value="{!u.index}" />
            </apex:column>

            <apex:column headerValue="isInternal" >
                <apex:outputText value="{!u.isInternal}" />
            </apex:column>

        </apex:pageBlockTable>

    </apex:pageBlock>
</apex:form>